THE FIRST part of this presentation began with definitions of the three kinds of health-related behavior. Health behavior is any activity undertaken by a person believing himself to be healthy, for the purpose of preventing disease or detecting it in an asymptomatic stage. Illness behavior is any activity, undertaken by a person who feels ill, to define the state of his health and to discover a suitable remedy. Sick-role behavior is the activity undertaken, for the purpose of getting well, by those who consider themselves ill. It includes receiving treatment from appropriate therapists, generally involves a whole range of dependent behaviors, and leads to some degree of neglect of one's usual duties.In the next step, a theoretical framework seeking to clarify behavioral accompaniments of changes in health was suggested. Within this framework, the changes in health and illness were seen from four levels of description: somatic health, behavior, role performance, ancl identity. Next, a theoretical model of action was proposed, which attempted to describe the important variables influencing health, illness, and sick-role behavior. The remainder of the paper was then concerned with reviewing studies of health and illness behavior so that the relevance and adequacy of the model of action could be evaluated. The focus of the present paper is on studies of sick-role behavior and the support they may provide for our theoretical framework.