The study examined the relationships among participation in outpatient rehabilitation, health locus of control, and mastery of stress with coronary artery disease A sample of 111 persons who had been hospitalized for coronary artery disease completed the Master of Stress Instrument (MSI) and the Multidimensional Health Locus of Control Scale One fourth of the sample had participated in the hospital's cardiac rehabilitation programme Results showed no difference between cardiac-rehabilitation participants and nonparticipants on mastery, internal locus of control or stress Demographic characteristics of age, education, race and gender revealed no significant correlation with either the total MSI score or its component measures However, internal locus of control was significantly and positively correlated to both growth and total mastery A stronger relationship was found between internal locus of control and change This finding supports the hypothesis that health-internals achieve higher levels of mastery