Much evidence suggests that intrinsic molecular or cellular aging mechanisms need not be invoked to explain most age-related cellular changes and pathologcical conditions. Analysis of a widely scattered literature indicates that hormones and neural factors regulate a great number of cellular aging phenomena of mammals. It is proposed that age-related changes after maturation result from an extension of the neural and endocrine mechanisms that control earlier development and that produce a regulatory cascade of changing neural, endocrine, and target-tissue interactions.