ASHINGTON, Feb. 5 — A survey of medical experts who write guidelines for treating conditions like heart disease, depression and diabetes has found that nearly 9 out of 10 have financial ties to the pharmaceutical industry, and the ties are almost never disclosed.

It has long been known that contact with the pharmaceutical industry can influence individual doctors' prescribing patterns and that financial support from drug manufacturers can affect the course of academic research.

But the survey, a relatively small study conducted by a team from the University of Toronto, is the first to document the extent to which the industry may influence so-called clinical practice guidelines. These voluntary guidelines, which are typically published in medical journals and endorsed by medical societies, set standards that are followed by countless doctors.

"These clinical protocols should be seen by the public as unbiased," said Sheldon Krimsky, a health policy expert at Tufts University who has written extensively on financial conflicts of interest. "The fact that there is a veil of secrecy over most of these does not bode well for a clinical community which is trying to ensure trust in the public."

The survey, in this week's issue of The Journal of the American Medical Association, sought the opinions of 192 medical experts who participated in writing 44 sets of practice guidelines covering treatment for asthma, coronary artery disease, depression, diabetes, high cholesterol, pneumonia and other ailments.

Of the 100 who responded, roughly 9 out of 10 had some type of financial relationship with a drug manufacturer, including research financing and speaking, travel or consulting fees. About 6 out of 10 had financial ties to companies whose drugs were either considered or recommended in the guidelines they wrote.

Eleven of the 44 practice guidelines were underwritten by pharmaceutical companies and carried declarations stating so. But of the 44 guidelines, just one reported a potential conflict of interest.

"That's a problem," said Dr. David Blumenthal, a health policy expert at Harvard Medical School who has written about financial conflicts in the medical profession. "This is just emblematic of the extensive, often undisclosed relationships that exist between medical experts and pharmaceutical companies."

Financial conflicts of interest are the subject of intense debate in medicine. Pharmaceutical companies often underwrite the cost of medical conferences and hire prominent academic doctors to serve as speakers or to lead symposiums at which the companies' drugs are discussed.

Proponents say the companies are helping to educate doctors. But critics have complained that such financial relationships jeopardize the integrity of scientific research. This week, more than two dozen prominent scientists and doctors sent a letter to more than 200 scientific journals urging them to strengthen their requirements for disclosing conflicts of interest.

Among those who signed is Dr. Marcia Angell, the former editor of The New England Journal of Medicine. In an interview today, Dr. Angell said that disclosing financial ties to industry was the least doctors could do and added that in most cases, the ties should be simply severed.

"Most consulting arrangements are simply a way for researchers to make money and the industry to buy their good will," Dr. Angell said. "Researchers serve on advisory boards and speakers' boards, and they travel around the world, ostensibly to educational programs. But really, they are just enriching themselves, and the drug companies retain influence over them to a remarkable extent."

Others, including Dr. Allan S. Detsky, an author of the Toronto study, take a less stringent view, arguing that conflicts should be made public and that doctors should discuss them openly before writing guidelines.

"It's not possible to stamp this out," Dr. Detsky said. "The answer is to sensitize people to accept that it's a problem."

Only 7 percent of the doctors in the Toronto study said they believed that their relationships with industry influenced their recommendations, although 19 percent said financial ties influenced the recommendations of their colleagues.

A spokesman for the Pharmaceutical Research and Manufacturers Association, an industry trade group, said today that the organization was not opposed to doctors' disclosing their ties with industry.

But the spokesman, Jeff Trewhitt, said drug companies did not want to see doctors with drug industry ties excluded from writing guidelines.

"Too many exclusions would mean not allowing some well-respected experts to work on these important guidelines," Mr. Trewhitt said.