Mortality from ischemic heart disease has declined in Japan since 1970. This paper addresses the declining mortality from ischemic heart disease and the possible contributing factors for 1956-1980. Mortality figures were obtained from Vital Statistics reports by the Ministry of Health and Welfare in Japan. National trends in blood pressure levels, prevalence of hypertension, Keys' lipid factor phi instead of the serum cholesterol level, and body mass index were obtained from the National Nutrition Survey which is carried out annually from random samples in Japan. The smoking rate which was obtained from other national surveys was also reviewed for this purpose. The age-adjusted (30-69 years) mortality from ischemic heart disease declined by 24% and 37% for men and women, respectively, between 1968 and 1978. It seemed that the decline in blood pressure levels and in the prevalence of hypertension and the increasing treatment rate for cardiovascular disease might contribute to the declining mortality from ischemic heart disease. The decline in cigarette smoking may, in part, also play a role. On the other hand, the increase in intake of lipids which resulted in Keys' lipid factor phi was compatible with the increase in mortality from ischemic heart disease during 1956-1970. The experience in Japan shows that the treatment of hypertension or the lowering of blood pressure and the recommendation to stop smoking help to prevent ischemic heart disease.