Brent Vose, head of oncology at AstraZeneca, is not sure whether Iressa, the Anglo-Swedish company's new drug for lung cancer, will be licensed first in the US or Japan. "That is an amazing change," he says, still pinching himself at the mere possibility of launching a drug in Japan.

Until recently, an experimental medicine discovered by a foreign pharmaceuticals company could not have hoped for Japanese approval until it had been tried and tested in the west for years.

Prozac, the anti-depressant that has become a household name in the west, has not yet been registered.

The fact that western companies are now lining up to get their drugs licensed shows just how much things have changed. AstraZeneca is just one of several foreign companies beefing up its salesforce at the prospect of a string of drug approvals.

Mr Vose attributes the change to two main factors. First, Japan has signed up to the International Conference on Harmonisation, which commits it to following good clinical practice as defined by international norms.

This means that Japan's long-standing insistence that clinical trials be repeated in Japan - to prove that drugs designed for Caucasians work on the Japanese - is becoming less tenable.

The practice is gradually giving way to the acceptance of foreign data supplemented by small "bridging studies" to show the results of western trials are meaningful in a Japanese context.

The result is that, instead of repeating lengthy and ferociously expensive clinical trials, western drug companies can rely on a single, international clinical trial programme. In theory, at least, this removes at a stroke one of the biggest obstacles to registering drugs in Japan.

"The regulatory environment has changed so dramatically, there's a great opportunity for companies...to get their drugs faster to market," says Derek Winstanly, president of Quintiles Japan, the clinical research organisation.

It works both ways, says Mr Vose. Results from Japanese trials are increasingly being accepted by foreign regulators as clinical trial practice is brought up to international standards.

Crucially, since 1997, patients have had to sign informed consent forms before joining a clinical trial - ending a practice of enrolling patients without their knowledge.

Although this initially made recruitment harder, there are signs that doctors and patients are growing used to the idea that Japan could gradually become an important international centre for clinical trials.

"In the past Japanese patients were reluctant to sign informed consent documents, but now if we advertise in newspapers a bunch of people put up their hands," says Kenjiro Nagasaka, chairman of Banyu.

The second reason for change, says Mr Vose, stems from new attitudes among what drug companies refer to as "key opinion leaders"; the oncologists, cardiologists and other specialists who set the tone for medical practice in any healthcare system.

Increasingly, these experts are studying abroad, says Mr Vose, and are changing the traditional Japanese outlook on medical intervention.

Japanese doctors have traditionally prefered drugs with fewer side-effects, even at the expense of efficacy. But many are now clamouring for the potent drugs that are widely used abroad, particularly in areas like oncology.

"Our bureau thinks that patients have not generally been well served because they were not able to access the innovative treatments that were available in other countries," says Daisaku Sato, deputy director of evaluation and licensing at the Ministry of Health, Labour and Welfare, the rough equivalent of the US Food and Drug Administration.

"This is why we strongly support the idea of International Conference on Harmonisation."

As well as approving foreign drugs, Japanese regulators have become harder on home-grown medicines for such conditions as dementia. Several medicines, huge sellers despite limited efficacy, have been withdrawn over recent years.

Mr Nagasaka of Banyu cautions that these undoubted improvements should not obscure the fact that regulation can still be idiosyncratic.

The difference can come down to which regulatory officer a company is dealing with, he says.

Most foreign companies have tales of drugs held up for years in the regulatory process - and others that move quickly to licence. Some executives hint that there is still a bias against their medicines, particularly if local companies have drugs in the same category.

"Japanese companies have always had a competitive advantage," complains a senior executive of a western company.

But asked if things are improving, the same executive replies: "Things are becoming more international, more scientific and more rapid. Of that there is no doubt."