To clarify the possible risk factors for the development of hypertension, we examined the influences of heredity and environment on blood pressure regulation and whether or not the physiological condition differed in high school students with different levels of blood pressure. A borderline hypertensive (BH) group, consisting of 75 male students with systolic blood pressure (SBP) consistently (N) group of 84 male students with SBP below 130 mmHg. In the BH group, 43% of students had a family history of hypertension within two generations of relatives, while 18% had one in the N group (p<0.05). The BH group was characterized by a gain in weight, a slight increase in 24-hour urinary sodium excretion, a higher heart rate, elavated values of plasma renin and urinary aldosterone, and an elevated sodium concentration in erythrocytes. Nevertheless, urinary excretion of potassium and kallikrein did not differ between the two groups. In each group, students with familial hypertension had a significantly (p < 0.05) lower 24-hour urinary kallikrein excretion than those without it. Although kallikrein excretion correlated fairly well with aldosterone excretion (r=0.47, p < 0.01) or creatinine clearance (r=0.59, p < 0.01) in the BH students without familial hypertension, no such correlations were found in those with familial hypertension. These results indicate that the abnormal relationships of aldosterone to kallikrein metabolism and of kallikrein to renal function control may be involved as hereditary factors in the development of hypertension.