Studies are being carried out on the effects of aging on cerebral protein synthesis and glucose utilization in rats. With the application of local methods developed in this laboratory discrete regions of the brain can be examined in normal conscious animals. The regional changes in glucose utilization indicate that entire sensory pathways are affected by the aging process. The fact that similar changes are found in the same pathways with respect to protein synthesis suggests that some of these changes reflect an adaptation of the nervous system to a chronic lack of input. The basis of some of the changes which occur with age can be further examined in studies with pharmacological agents as well as in conjunction with behavioral measurements. Two such studies have been undertaken. One is a study of the effects of aging on the metabolic responsiveness to the dopaminergic agonist, apomorphine. The other is a study of the effects of environmental enrichment in young adult rats on local metabolic rates. In both of these studies the end point is the local rates of cerebral glucose utilization as determined by the deoxyglucose method.