Objectives: To study the relation of type A behavior pattern and job-related psychosocial. factors to the risk of myocardial infarction. Methods: Study subjects comprised 290 cases (173 male workers and 117 women) of nonfatal acute myocardial infarction (AMI) and 489 controls (303 male workers and 186 women) recruited from among residents of the study area. Participation rates of cases and controls were 86% and 50%, respectively. Type A behavior pattern, job-related psychosocial factors, and other coronary risk factors were ascertained by interview using a questionnaire. Type A behavior pattern was measured by 12 questions, and job strain by the method of Karasek. Logistic regression analysis was used to calculate odds ratio and 95% confidence interval with adjustment for potential confounding variables. The relation to job strain was examined only in men. Results: Type A behavior pattern was significantly associated with an increased risk of AMI in male workers (adjusted OR = 1.9, 95% CL 1.2-2.9) and in women (adjusted OR = 2.8, 95% CI, 1.6-4.9). Although job control and job demand showed no material association with AMI, job strain, a combination of low job control and high job demand was associated with an increased risk of AMI (adjusted OR = 2.2, 95% CI, 1.1-4.5). Abbreviated type A score and job demand score were higher among nonparticipant control candidates than participant controls in male workers. Conclusions: Type A behavior pattern may be an important risk factor for AMI especially in Japanese women. The present study also revealed persons in stressful psychosocial circumstances were less likely to participate in the study.