A team of University of Michigan doctors has confirmed that cyclosporine, the powerful drug that prevents organ rejection in transplant patients, can clear up the thick, scaly patches of skin that characterize psoriasis.

The study, published in the New England Journal of Medicine, is the first to suggest a proper dose of the drug.

In tests on 85 volunteers, a group led by Charles Ellis was able to eliminate almost all the patches in four of five patients who received a daily dose of 7.5 milligrams per kilogram of body weight.

Although they did not directly compare cyclosporine treatment to other therapies, such as the combination of drugs and ultraviolet light, the researchers said the therapy seems to be at least as effective as standard treatments.

But because cyclosporine can increase the risk of cancer or cause kidney problems or other serious side effects, cyclosporine is not likely to become the main treatment for psoriasis.

"In the short term, {the effect on the kidneys} is easily reversible," said Ellis, a pro- fessor of dermatology at the university's medical center.

"There are studies in progress to determine whether cyclosporine can be used on a long-term basis," said Ellis.

Nicholas J. Lowe of the UCLA School of Medicine agreed that such studies are needed.

Cyclosporine "should probably be used only as a short-term therapy until more clinical experience is reported," he said in a companion editorial.

About one in 50 Americans and Europeans have at least some degree of psoriasis, and in one out of 250 people the condition is severe enough to require drug treatment. The patches of inflamed red skin, often covered by silvery scales, usually appear on the knees, elbows, trunk and face.

The scales appear because the body's normal process of renewing and shedding skin cells is accelerated.

Among the complaints from patients taking the drug were fatigue, stomach and intestinal problems, muscle or joint pain and flu-like symptoms.