The relationship between blood pressure and ECG findings (Minnesota Code) were studied in 1906 subjects aged from 35 to 65 in 1966 in three districts of Okayama prefecture from 1966 to 1976. Following results were obtained; 1. Comparison of the mean values of blood pressure (of 918 subjects, 307 male and 611 female) between the first half (1966-1970) and the second half (1971-1976) period showed that the blood pressure fell in the majority of patients with moderate or severe hypertension but elevated in 13-15% of subjects with mild hypertension (satisfying both the systolic blood pressure of 180 mmHg and the diastolic blood pressure 100 mmHg). Both improvement and aggravation in blood pressure were more frequent in male, while in female blood pressure level mostly remained unchanged. Blood pressure in the plane district (Osahune-Cho) was the most favourable than that in other two districts. 2. Along with an elevation of blood pressure, Code 1-0 in ECG decreased and codes for left ventricular hypertrophy (combination of two or more subcategories of Code 3, or of Code 3 with Code 4 or 5) increased. Code 1-0 decreased with aging, while prevalence rate of Code 4 or Code 5 was affected neither by aging nor by blood pressure. 3. The ECG code suggesting left ventricular hypertrophy closely related to systolic blood pressure.