ROCHESTER, N.Y., JUNE 30 -- Within the next year, a dozen or more research centers across the United States may begin to use a relatively new procedure to try to arrest Parkinson's disease -- transplanting bits of tissue into the brains of people with the affliction, several researchers predicted today.

The increase in the operations will occur even though the effectiveness of the procedure has yet to be proved.

Mexican researchers last April reported glowingly positive results from the transplant procedure, sparking "a very great push" from patients desiring the transplant oepration, according to Dr. Lars Olson, an early transplant researcher from the Karolinska Institute in Stockholm.

But U.S researchers have not duplicated the Mexican results. And some researchers gathered here at the Schmitt Neurological Sciences Symposium said they are skeptical of the Mexican reports because other research into the procedure in Sweden and elsewhere has not produced the highly positive results that Mexico has reported.

Between 500,000 and 1 million Americans suffer from Parkinson's disease, which causes rigidity, shaking and difficulty in walking. The disease occurs when the portion of the brain that produces dopamine is destroyed -- either as a result of aging or, in some cases perhaps by pollutants.

Surgeons have been transplanting a portion of the adrenal gland, which is attached to the kidney, into the brain. When it is transplanted, the adrenal cells produce dopamine, the chemical lubricant of voluntary motion.

There are a half-dozen centers around the world that have performed the transplants on 44 patients, three of whom have died.

The most startling results came from Mexico, where Dr. Rene Drucker-Colin of the Universidad Nacional Autonoma de Mexico reported improvement in 11 of 18 patients, including several who improved markedly. One 35-year-old went from being barely able to walk to being able to tend his small farm after transplants.

But, at Vanderbilt University Hospital in Nashville, Tenn., where six patients have received transplants, George Allen, the surgeon who led the Vanderbilt team, said "we can reach no conclusions at this time" about how well the procedure worked.

Several researchers expressed surprise and doubted Drucker-Colin's results. "I do not find it convincing," one scientist said. "It is so dramatic that it leads one to question."

"There was an evident benefit," Drucker-Colin said. "I would say that the patient's tremor has practically disappeared."