Neurotrophic factors are now recognized to play important roles in the normal function of the mature central nervous system. This knowledge has motivated experiments to evaluate the potential benefits of administering neurotrophic factors to the aged brain. This article provides a review of studies to date that have determined the behavioral effects of such treatments. Nerve growth factor (NGF) administration appears to reliably enhance learning and memory in aged rats, while glial-derived neurotrophic factor (GDNF) causes some improvement in motor function. Problems associated with neurotrophic factor administration to humans are discussed.