The blood pressure of humans varies from a low level with a narrow range of distribution remaining so throughout life to a high level with a wide distribution(e.g., the inhabitants of Northeast Japan). The author made a longitudinal epidemiological studies on hypertension in three farm villages (O.K.and N.) in Northeast Japan. Blood pressure was determined once or twice a year by mass surveys from 1954(O),'58(K) and '57(N) respectively up to 1975. According to the results obtained in the person-years of obsevation at every 10 mmHg level is the blood pressure of 760 males and 899 females in the 40 to 69 years of age, it becames obvious that persons whose blood pressure were around 120 mmHg for the systolic and around 70 mmHg for the diastolic were lowest in the death rates. By a regression analysis of longitudinal trends in blood pressure it was recognized that the level and the trend differes individually. The salt intake of the Japanese population is influenced by its tranditional eating habits and the Japanese, especially the　 inhabitants of Northeast, consumed 20-30 g of salt per day. Intervention studies on control by reducing high salt intake have been carried out. The level of blood pressure of the inhabitants tends to become lower compared at the begining in the 1950's and the changes in the dietary pattern related to high salt intake were observed and in the group of　person whose high salt intake lasted 20 years the level of blood pressure arose and the distribution of blood pressure got wider with advance in age.