Type A behavior pattern was assessed using the structured interview and hostility level was assessed using a subscale of the Minnesota Multiphase Personality Inventory in 424 patients who underwent diagnostic coronary arteriography for suspected coronary heart disease. In contrast to non-Type A patients, a significantly greater proportion of Type A patients had at least one artery with a clinically significant occlusion of 75% or greater. In addition, only 48% of those patients with very low scores (less than or equal to 10) on the Hostility scale exhibited a significant occlusion; in contrast, patients in all groups scoring higher than 10 on the Hostility scale showed a 70% rate of significant disease. The essential difference between low and high scorers on the Hostility scale appears to consist of an unwillingness on the part of the low scorers to endorse items reflective of the attitude that others are bad, selfish, and exploitive. Multivariate analysis showed that both Type A behavior pattern and Hostility score are independently related to presence of atherosclerosis. In this analysis, however, Hostility score emerged as more related to presence of atherosclerosis than Type A behavior pattern. These findings confirm previous observations of increased coronary atherosclerosis among Type A patients. They suggest further that an attitudinal set reflective of hostility toward people in general is over and above that accounted for by Type A behavior pattern. These findings also suggest that interventions to reduce the contribution of behavioral patterns to coronary disease risk might profitably focus especially closely on reduction of anger and hostility.