We investigated, by case-control study, the relevance of psychosocial factors on the prevalence of acute ischemic heart disease (IHD) in middle aged Japanese men. We questioned 109 acute IHD patients and 80 individuals in an age-adjusted sampled control group. Multiple logistic regression analysis showed the following statistically significant factors: hypertension (odds ratio 4.01, p less than 0.001), Type A behavior pattern (2.25, p less than 0.05) and high job demand (2.23, p less than 0.02). No direct influence of family function or social support to the prevalence of acute IHD was apparent. These results suggest that, among men in Japan, Type A behavior pattern and high job demand represent psychosocial risk factors of IHD. Due to the case-control protocol, causal relationships cannot be decided. The limitation of the study design is discussed within that context.