The role of nerve growth factor in stimulating cholinergic function, loss of which is a cardinal feature in Alzheimer's disease, has been documented for many years from preclinical animal model studies. This anabolic growth factor has been delivered into the forebrain of patients with mild Alzheimer's disease using transfer of autologous fibroblasts engineered to produce nerve growth factor. A Phase I clinical study shows that fibroblast transfer and growth factor expression is well tolerated and the rate of cognitive decline in patients is improved, correlating with an increase in metabolic activity detected in the cortex.