Patients who have had scores of tests for unexplained conditions that doctors have so far been unable to diagnose may yet have treatment options under a new National Institutes of Health initiative.

A director of the Undiagnosed Diseases Program, William Gahl, said he expects the NIH effort will be a way for physicians to discover new diseases — and then attempt to begin finding cures for them.

Recent advances in genetics — including biochemical genetics, or the study of “inborn errors of metabolism” — and the completion of the human genome map are allowing medical researchers to pinpoint many genetic defects and diseases that until recently were undetectable. This is why geneticists such Dr. Gahl will form the cornerstone of the NIH program announced last week.

Dr. Gahl has conducted research and treated patients at the Bethesda, Md., medical complex for 25 years. He has an office drawer filled with unexplained combinations of symptoms for which there are no known medical explanations. When asked to pull a random case file from the drawer, Dr. Gahl pointed to an instance of abnormally shaped blood platelets that doctors at the NIH had never before seen in a patient.

The idea behind the Undiagnosed Diseases Program is that, with blood platelets, for example, hematologists may have come across more than one instance of a similar condition. If the NIH program can detect examples of the condition in more than one member of a family, then patients can know, at the very least, that they have a genetic disease on their hands.

“But it’s a new disease that you won’t find anywhere in the genetic literature,” Dr. Gahl said. “Sometimes a person will get, say, a muscular disease that he’ll attribute to the environment, like living above a ‘Love Canal’ situation. In most cases, though, it’s genetic.”

The NIH plans to admit just 100 patients to the on-site program; children will account for about one-third of the enrollment. “We’ll be very selective when it comes to patient eligibility. Our focus is strictly on conditions that haven’t been diagnosed,” he said.

The most significant reason for the stringent screening process is because the majority of people who think they are sick with an undiscovered disease simply haven’t been diagnosed properly, according to Dr. Gahl. The NIH also expects that hypochondriacs — that is to say, physically healthy people who nonetheless worry excessively about being sick — will naturally apply to the program.

“There will be a mixed bag of applicants,” he said. “Some of them should have had more tests locally; it’s only a matter of receiving the right test to discover the disease. And then others will actually have new diseases.”

In addition to Dr. Gahl and his team of geneticists, there will be 25 specialists in the NIH program, including doctors specializing in endocrinology, immunology, oncology, dermatology, dentistry, and cardiology. They will all attend a regularly scheduled board meeting to consult with each other about the patients in the program. “We’re taking advantage of intellectual synergies,” Dr. Gahl said.

“This is an important project that will assist patients with undiagnosed disorders that run in families,” the chairman of the Department of Genetic and Genomic Sciences at the Mount Sinai School of Medicine, Dr. Robert Desnick, said. “If the genetic defect is identified, then it may be possible to develop therapies using a variety of new techniques.”

The NIH program could also be a boon for pharmaceutical companies developing new drugs, according to Brad Kloza, a director of ScienCentral, a Manhattan-based firm covering scientific research for local broadcast news affiliates.

“New diseases can’t be a bad thing for pharmaceutical companies. But the specifics of what’s discovered will determine whether or not it’s a particularly good thing,” he said.

Mr. Kloza said big pharmaceutical companies don’t often invest a lot of money looking into cures for rare diseases because the payoff can be too low. “You would tend to assume that undiscovered diseases are rare ones,” he said.

On the other hand, pharmaceutical companies are good at finding new markets for existing drugs, and those new markets often come from the discovery of new, rare diseases, Mr. Kloza said.