She came to a gathering of the world's leading brain transplant neurosurgeons looking for a miracle. Her husband, himself a biologist, has severe and progressive Parkinson's disease. They had been studying the transplant options for some time and had made a tentative decision: he wanted a human fetal brain cell transplant, even though it has never been done, and she had come looking for a surgeon to do it.

They even had their own source of fetal cells. The couple's two daughters had agreed to become pregnant and abort the fetus to provide transplantable brain cells for their sick father.

On the face of it, the daughters' decision was reasonable, a choice to help the man who gave them life and love. To the medical community, already concerned about the ethical implications of brain tissue transplant surgery, the prospect of growing a fetus with the intention of aborting it in order to transplant cells from its brain is more than many physicians want to face.

Yet, from Parkinson's to diabetes, from blood disorders such as leukemia and sickle cell anemia to severed spinal cords, reseachers have discovered that the hardy cells of a fetus can be transplanted into an adult body and thrive. Their immaturity seems to help protect them from rejection, and their youth and vitality allows them to grow and take over functions lost by disease.

Fetal cells may prove the best choice in brain transplants, and they already have been tried in human patients. After the nuclear power plant accident at Chernobyl, six victims received fetal blood cells to help restore their battered immune systems; the transplants, however, failed. Denver doctors transplanted fetal pancreatic cells into nearly two dozen diabetics in the hopes that the fetal cells would take root and begin producing insulin, a hormone missing in one form of that disease. Initial results have been promising.

Despite tentative success and the talk of possible cures, researchers fear that many Americans will be horrified by the idea of transplanting cells from aborted fetuses, and that there probably will be a long and bitter debate before fetal transplants enter the mainstream of medical practice.

Some scientists, however, already have staked out their position. "You have fetal tissue cast away," said Dr. Alan Fine of the Medical Research Council in Cambridge, England. "It could benefit patients with a terminal disease. There is a clear ethical position, which is to use it."

But others have begun to think about how society will respond. "People will say that it sounds wrong," said Dr. Robert Levine, an ethicist at the Yale University School of Medicine.

The intuition that it "sounds wrong" is a warning flag that the issue needs to be examined carefully; it does not mean that it is wrong, Levine said.

"The law does not prescribe motivations for conceiving a fetus," he said. "Most of us grew up with an understanding of why one conceived. Most commonly, it is to have a baby. When one says, 'Let's have a fetus so we can get substantial nigra {brain tissue} after we abort it, that somehow strikes us as alien. But by what grounds can we say it is wrong? It is not illegal. We have a law that says we cannot stop a woman from having an abortion for whatever reasons she finds necessary."

This is an area of debate in which politics will probably play a greater role than science, Levine said. "Right now, we have no formal mechanisms in place to consider matters of this sort at a federal level."

Bioethical standards governing life-and-death issues cannot be easily applied to the transplantation of fetal cells. Normally, the Uniform Anatomical Death Act says organs cannot be taken from a cadaver until it is declared brain dead. To use fetal cells for Parkinson's disease, however, the brain needs to be alive to produce viable tissues for transplantation.

The question, then, is: When is the fetus dead?

Every year, an estimated 1.5 million fetuses are aborted. Research suggests that the best brain tissue comes from a 9-week-old fetus. If a suction abortion is performed in the first trimester and the fetus is dismembered by the process, then it cannot be considered alive or viable, even if the brain remains intact and briefly alive, several researchers said. With fetal transplants, it may also be possible to use the cardiovascular criteria for being dead.

What intensifies the ethical debate is the idea that "one could plan ahead of time to get pregnant to supply a cadaver," said Dr. George Allen, a neurosurgeon performing transplants at Vanderbilt University Medical Center. "The analogus situation is in an adult where a mother says, 'I have two daughters and am willing to donate one of their hearts.' We would say that is murder, pure and simple."

If fetal cell transplants are proved successful, but are blocked in the United States on ethical grounds, some, like Judy Rosen of the United Parkinson's Foundation in Chicago, believe that patients would travel to Sweden or England, where such experimental human treatments are planned. That, said Rosen and several scientists, raises the issue of the rich being able to get what is potentially a better treatment because they can afford to go to Sweden, while the poor are left with a less effective treatment here in the United States.

These issues, said Yale's Levine, "are about as complicated as any I've run into."