The literature relating to the learned control of autonomic processes, especially cardiovascular processes demonstrating that the activities of visceral response systems may be modifi ed by operant reinforcement and biofeedback procedures, has grown exponentially. This research seems to show behavioral properties in the cardiovascular system that were previously believed to be exclusive attributes of the somatic response systems; the implications of this for possible therapeutic use have received widespread publicity. Questions remained unanswered-about the nature of "voluntary" control and the conditions necessary for establishing it, the reciprocal effects of conditioned changes in cardiovascular and psychological or behavioral functioning, the use of cardiovascular events to index behavioral states, and the principles and techniques whereby operant conditioning of the cardiovascular system can be clinically applied.