Neural transplantation: a call for patience rather than patients.

Research into embryonic cell grafting in human subjects suffering from Parkinson's disease should not repeat the mistakes made by adrenal autograft investigators, who operated on far more humans than on nonhuman primates because of a single unconfirmed report of dramatic improvement in two Mexican patients. Citing extensive data from experimental transplants conducted as early as 1944, the authors argue that, until a sufficient number of animal studies have been performed to answer many crucial questions about human fetal tissue transplants, researchers should refrain from experimenting on human patients.