This could almost be boiled down to five websites: NHS Direct; Patient UK, a site run by two Newcastle family doctors; Healthfinder, which is a site sponsored by the US government; MEDLINEplus, which includes the site of the US National Library of Medicine; and, for keeping up to date on what's available and for issues surrounding health on the net, He@lth Information on the Internet, a site run by Robert Kiley, information service manager at the Wellcome Trust. Kiley is also the author of Medical Information on the Internet: A Guide for Health Professionals which is a perfect starter guide for more serious health consumers who want not only a good grounding in how to look up the odd piece of health or medical information but also to become relatively, or very expert. It's available from www.amazon.co.uk for £19.95 and is kept up to date at www.hbuk.co.uk/kiley.

You can of course just set off to look for what you want using a standard search engine or, in the portal-type sites, their health categories. The former will provide a huge number of results that you will have to trawl through, unless you can define your search with some precision. The latter will give you the search engine's selection, including lots of commercial sources for information. A more focused approach can be tried through the following.

NHS Direct Online (www.nhsdirect.nhs.uk)

This is the official NHS website, and at the moment is listed as much for its potential as for what it can already do. After a somewhat clunky start, this looks like being one of the things the NHS has got right, and there are big plans for it. It provides the phone number for the nurse-led helpline of NHS Direct itself: 0845 4647 - a service that will cover the whole of England by the end of 2000. But it provides much more than that.

There is an online healthcare guide with simple advice about a range of conditions, and which can tell you within half-a-dozen clicks to ring 999 if that band of pain around your chest looks like being a heart attack. At the moment the clinical section is limited. But there are plans to link it into the computer-led protocols that the nurses in NHS Direct call-centres use, across the whole range of conditions, to advise people whether to self-treat, visit a pharmacist, see a doctor, go to an accident and emergency department or ring 999.

It contains a monthly health feature, which is archived - a recent one was on travelling abroad - and contains lots of useful links. And its Conditions and Treatment section has links to many hundreds of patient organisations and self-help groups - the links take you to their websites where they have them, and to an online version of patient information leaflets where they exist. If an organisation is not yet on the web, it provides phone numbers and contact addresses, plus the price of hard copy leaflets and books.

The websites to which NHS Direct Online links have been quality checked by Omni, an organisation that seeks to provide a UK gateway to quality information on the net but which is aimed more at professionals than consumers. The leaflets to which the site points have been given a star rating for quality by the Centre for Health Information Quality (www.hfht.org/chiq). There is also a Hot Issues button, which changes every day and is a good way of checking out the latest health stories or health scares - the decision to advise the removal of soya oil breast implants, for example, or the latest pill or vaccine issue. It lets you see what the health department actually said, not just what the media reported.

This is an official NHS site. But its policy to date has been to be open about disagreements over what the NHS should and should not do. So, to take a recent example, the site links into the Multiple Sclerosis Society (www.mssociety.org) which believes that beta-interferon should be much more widely available, despite the provisional view of the National Institute for Clinical Excellence (www.nice.gov.uk), that it should not.

At the moment, NHS Direct Online does not include a search engine to find your local hospital or doctor, but that is planned for the end of the year - complete with maps to find both them and local support organisations. From next year, NHS Direct Online plans to offer e-mail consultations with the nurses who provide the backbone of NHS Direct itself.

There are also plans for NHS Direct Online to form the "ground floor" of a much more extensive electronic health library, assembling internet resources from around the world primarily for health professionals. The current intention, however, is that patients and the public will also have access to those tiers. The site is still a long way short of perfection, but it is popular and should develop - about 30,000 people a week visit it at present.

Patient UK (www.patient.co.uk)

Run by two Newcastle-upon-Tyne GPs, this site is, in a sense, a private enterprise version of NHS Direct without the online diagnosis, but not a commercial one, although it has become so large that it is having to explore commercial links such as advertising and e-commerce to keep going. Extremely clearly organised and easy to use, it operates in tiers.

For each disease or health topic, it points patients first to patient-oriented material and to support groups. It provides information on drugs. It then offers links to professional guidelines, original articles in journals and to other evidence-based sources of information including Medline and professional sites such as Bandolier (www.jr2.ox.ac.uk/bandolier).

Unlike NHS Direct Online, it also provides information on private sources of healthcare, and through a link to Scoot can help you find the phone number and address of anyone from your local doctor, chiropodists or dentist, to local hospital or hospice. The site is a labour of love and remarkably comprehensive.

For UK patients, it has the great advantage of being UK-oriented. If it is only information you are after, it might be all you ever need. When using it, clicking the More Options button on the left opens up the site.

Healthfinder (www.healthfinder.gov)

This is, in effect, the US equivalent of NHS Direct, but without the online diagnosis guide. Older and longer established than NHS Direct, it does much the same thing on a far grander scale, linking to many thousands of reliable sites. Its sheer scale makes it less easy to navigate than it was, but it is a huge resource visited by 450,000 people a month.

It chiefly points to US sites, however, and while there is much in common between US and UK medicine, there are cultural differences between the two. Individuals within both countries vary, but it is probably fair to say that on balance Americans have a more heroic attitude to healthcare interventions than people in the UK. You can, for example, through Healthfinder, find resources that advocate bone marrow transplantation for disseminated breast cancer, an experimental treatment you are unlikely to get on the NHS on the grounds that it is unproven. Equally, some US professional groups recommend more frequent screening for breast cancer than the NHS provides - an issue where professional disputes around the evidence remain. One of the key sites that Healthfinder points to is the following.

MEDLINEplus (www.medlineplus.gov)

This is the place to be if you are deeply serious about health on the net. It is one of the top 250 most visited sites on the internet and provides a cornucopia of accurate and current medical information, linked directories of US patient organisations and web-published leaflets, plus access to the online version of the US National Library for Medicine. It is well designed and easy to access. It also has an online illustrated medical encyclopaedia and medical dictionaries, plus the National Institute of Health's database of clinical trials at www.clinicaltrials.gov.

If you want to read the latest original research, MEDLINEplus, through PubMed, gives you access to the US National Library for Medicine database, which contains abstracts of more than 11m medical articles from around the world. It is here that things can get costly and complex. While abstracts are available free, only some journals offer any articles in full for no fee. And even then the number of articles available is limited. MEDLINEplus has a document ordering system: the costs vary by journal, and few journals have internet delivery of text. You may well have to go through the British Library to receive full texts - MEDLINEplus provides all the links you need to do that.

But be warned, searching PubMed - as opposed to MEDLINEplus - is no easy task for a beginner. It has recently become more user-friendly and a guide for the more expert on what it can now do can be found at the following.

He@lth Information on the Internet (www.wellcome.ac.uk/healthinfo)

A site sponsored by the Wellcome Trust and the Royal Society of Medicine, Health Information on the Internet does not itself contain specific health information. Instead in six issues a year, all of which are archived and online, it keeps you up to date with what is available on the net and how to use it. While aimed at health professionals, researchers and managers, it contains a wealth of information of interest to consumers who want to know what's new, what's available and what the current issues are. Its June issue, for example, includes a guide to PubMed's new search engine, an article on quackery on the web, a guide to pharmacy resources on the internet, a discussion of internet privacy, and a list of new sites.

If these, in a sense, are the top five sites which are almost certain to last (in the case of MEDLINEplus virtually guaranteed to last as an in-depth quality guide to health), there is a host of other sources of information available. For mental health the top site is www.mentalhealth.com.

As mentioned, the big portals such as Yahoo! (www.yahoo.co.uk) as well as Excite (www.excite. com), Lycos (www.lycos.co.uk) and many of the others have health sections that are improving in depth and width all the time. Also worth a look is www.achoo.com.

Their rivals, however, are the commercial specialised medical sites that are beginning to do what the above do, only better. For many people, these may be among the best first ports of call. They are growing in number, but the better sites include the following:

Net Doctor (www.netdoctor.co.uk)

Net Doctor is one of the best of the UK "Doctor on the web" sites, while stopping short of individual diagnosis and treatment. It includes not only the now standard medical encyclopaedias and health advice, plus information leaflets for patients on medicines, but a summary of medical news and a growing number of self-tests with which you can amuse or alarm yourself. You can for example, work out your propensity for diabetes and whether you are (or might be) an alcoholic. There are even tools that are used daily by doctors such as Goldberg's depression test. You can e-mail questions in, joindiscussion groups with UK medical specialists when they're online, keep an eye on the latest medical news, contact support groups and find links to other medical sites. You can also get a summary of the daily newspaper health stories e-mailed to you overnight from the first editions.

It has been running for almost three years. But it's not perfect. At the time of writing, putting alopecia (patches of hair dropping out) into its search of diseases and conditions produced information about standard male pattern baldness (going bald, to you and me) but nothing specific on alopecia. It is none the less a rich site. It contains a short but useful guide to the NHS and, like Patients UK, a database of NHS organisations and private hospitals with phone numbers and addresses. But again, at the time of writing, while it boasts web links to those NHS organisations that have websites, there are at least some that do have sites where Net Doctor doesn't yet highlight the link. That is not necessarily entirely its fault (see NHS section below). It's a commercial site, but claims (and on the face of it appears) to aspire to high ethical standards. It subscribes to the code of conduct of HoN - Health on the Net.

Health on the Net (www.hon.ch)

A Switzerland-based website, Health on the Net is both a major international resource in its own right and a campaigner for high-quality medical and health information on the net. It has its own code of conduct and logo to which other websites can subscribe. Finding the HoN logo is a pretty good guarantee that the site is reliable - but its absence does not necessarily mean a site is poor. Healthfinder, for example, is HoN accredited, but NHS Direct hadn't bothered at the time of writing. Along with Omni and Discern it is one of a number of organisations attempting to kitemark health information. Omni's criteria for evaluating sites can be found at omni.ac.uk/agec/evalguid.html while Discern is at www.discern.org.uk.

Health in Focus (www.healthinfocus.co.uk)

Another doctor-backed UK commercial site, subscribing to the HoN code of conduct. It provides a similarly wide range of health-related information to Net Doctor, links to support groups and the like, all very much in the context of the UK health system. It is designed to make life easier for patients and for doctors who have to face patients armed with swathes of health-related information trawled from the net. It includes useful advice about what to think about before you go to see your doctor, and help afterwards, and is easy to navigate and clear. It contains advertising and links - currently for alternative therapies, Bupa and Amazon, but has an impressive editorial board and is easy to navigate. Health in Focus is also developing pages that work on web-to-speech and web-to-braille browsers for the visually impaired.

Surgery Door (www.surgerydoor.co.uk)

This is another commercial UK gateway to health information, launched in February 2000. Offering a similar, though different, mix to Health in Focus and Net Doctor, it is as yet less impressive, although some people prefer it. It does, however, have some useful bits and pieces such as a link to the Benefits Agency, detailing benefits and entitlements around health from free prescription entitlement to the carer's benefits, attendance allowance and other health and disability-related benefits. Application forms are downloadable where the BA makes them so.

It too subscribes to HoN, although its commercial nature is more in-your-face than Net Doctor. It has a shopping mall on its home page, for example, with links to a UK online pharmacy, and to www.condomaniadirect.com, an online discount condom and contraceptive store which, at the time of writing, aside from both standard and fanciful fare, was offering South Park condoms (your choice of Chef, Stan, Kyle, Kenny or Cartman) plus the chance to go on a planned Channel 4 programme if you have an unusual and exotic condom collection. There are also links to not so obviously health-related sites (unless you're visiting someone in hospital) such as Thornton's chocolate and Interflora. A US site that covers the same sort of territory, with moderated discussion groups and which subscribes to the HoN code is www.mediconsult.com.

British Medical Journal (www.bmj.com)

Finally, if all you want to do is keep track of what is happening in medicine, there's the British Medical Journal's website. The BMJ is one of the world's top four general medical journals and, unlike its competitors, The Lancet (www.thelancet.com), the New England Journal of Medicine (www.nejm.org), and the Journal of the American Medical Association (jama.ama-assn.org), it offers free full text articles, fully searchable back to 1994 on a site that has rightly won awards. Although policies in this area change as publishers of paper journals struggle to work out how to cope with the internet, the other three at present only offer contents, abstracts and search facilities free, with a subscription required for full text.

Other useful sites include www.hebs.scot.nhs.uk, the site of the Health Education Board for Scotland, which is full of good, fun stuff on healthy living and health promotion, some of which might even impress your children. Sex education for teenagers is available at www.lets-talk-about-sex.co.uk, while the BBC's coverage of health news, links to its broadcast programmes and large doses of health information and links are available at www.bbc.co.uk/health/.

If you want to get really serious about medical matters, you can also find a full general medical textbook online. The Merck Manual of Diagnosis and Therapy can be found at www.merck.com. Although this is the website of the pharmaceutical company Merck, and the textbook bears its name, it is none the less an impartial guide and one of the most widely used general medical textbooks in the world.

Another site to watch is www.medem.com, a commercial undertaking being launched by the American Medical Association in conjunction with nine other US medical colleges and professional organisations. It will provide links through US patients' own physicians. Its development may offer an object lesson and, if its commercial nature goes wrong, a warning of what could be coming in the UK.

Finally, if you want to know what is going on at the cutting edge of medical research, there are four big databases of clinical trials. None of these are descriptive of what is happening or why. They're intended for doctors, scientists and other health-related staff. The big US site is www.clinicaltrials.gov.

The UK equivalents include the National Research Register, of ongoing and recently completed research projects funded by, or of interest to, the NHS. It holds information on more than 50,000 projects and is expected to grow further. It includes entries from the Clinical Trials Register of the Medical Research Council (www.mrc.ac.uk) and details on reviews in progress collected by the NHS Centre for Reviews and Dissemination. This is available at update-software.com/nrr - click on the National Research Register button. There is also Current Controlled Trials at www.controlled-trials.com.

From these, you can find out who is conducting which trial and - if you are sufficiently dedicated and worried - you could approach the researchers to be included. UK doctors may prove less receptive to volunteers than US ones. And remember that many of these are randomised, controlled, double-blind trials - in another words, neither the researchers nor the patient knows whether they are receiving the new treatment rather than an older one or a placebo. The reason is to remove observer bias from the result. But it means that even if you join such a trial, you only have a 50/50 chance of receiving the new treatment. It is the way medicine progresses.