The degeneration of cholinergic neurons may be responsible for cognitive impairment in patients with Alzheimer's disease (AD). Since nerve growth factor (NGF) plays an important role in the survival and maintenance of cholinergic neurons in the central nervous system, this factor may have some beneficial effects on the cognitive impairment observed in patients with AD. However, since NGF does not cross the blood-brain barrier and is easily metabolized when administered peripherally, it can only be used when directly injected into the brain. In this review, we show that repeated oral administration of the NGF synthesis stimulators, idebenone and propentofylline, partially restored the age-associated decrease of NGF in the frontal and parietal cortices. Furthermore, this treatment attenuated the impairment of performance in the water maze, passive avoidance, and habituation tasks in rats with bilateral forebrain lesions, and in rats which had received continuous infusion of anti-NGF antibody into the septum. The behavioral improvement induced by idebenone and propentofylline was accompanied by recovery of both the reduced activity of choline acetyltransferase and the changes in [3H]QNB binding. These results suggest that the use of NGF synthesis stimulators may provide a novel therapeutic approach to cholinergic dysfunction.