Trends in age-specific and age-adjusted blood pressure and the prevalence of hypertension were obtained from the National Nutrition Survey of Japan, 1956-1980. The national trends in the age-adjusted blood pressure of people (30-69 years old) in Japan during the 1956-1980 period show an increasing pattern reaching a peak around 1964 followed by a decreasing pattern. To explore the possible factors which have contributed to the change in blood pressure levels, we analyzed the relationship between the blood pressure and several possible factors, including the rate of treatment for cardiovascular diseases (CVD) for men and women, annual salt and alcohol consumption per captia and body mass index (MBI) for men and women. Only alcohol consumption was considered in the analysis of men because women in Japan still tend to drink relatively little alcohol. In simple descriptive analyses, the increasing trend in the treatment rates of CVD seemed to be related to the decrease in the blood pressure level and in the prevalence rate of hypertension for both men and women. The impact of treatment rate seemed to overcome the adverse influence of the increasing trends in BMI. Recent decrease in salt consumption may account in part for the later period of the decreasing trends in blood pressure level and the prevalence of hypertension. In multiple regression analysis using these time series data, CVD, BMI and alcohol consumption were significantly related to blood pressure level and the prevalence of hypertension, although salt was not significant in these analyses.