Curt Richter made seminal contributions to our understanding of a number of issues regarding the relationships between physiology and behavior. He was the first to conceptualize behavior as an aspect of regulatory physiology. These ideas developed from his work on behavioral responses to a variety of physiological perturbations. The classic example is Richter's demonstration of the development of avid sodium ingestion in response to urinary sodium loss after adrenalectomy. Some of Richter's ideas on the nature and underlying physiology of specific appetites maintain their influence and continue to stimulate active investigation. Others, focused on abilities to self-select balanced diets, have not borne the test of time or experimental challenge. As current research takes a more molecular focus, Richter's ideas on behavior in the service of the internal milieu maintain their currency, and the search for the molecular bases for these relationships should serve as a research focus.