Plasma renin activity (ORA) was determined by radioimmunoassay in 55 normal controls and 121 hypertensive patients in basal state and after double stimulation with furosemide administration and upright posture of 4 hrs. The results were obtained as follows, 1) Mean value of PRA of normal control was 2.2+/-1.41ng/ml/hr in basal state and 2.9+/-1.39ng/ml/hr after double stimulation, respectively. The latter was elevated significantly as compaired to the former. 2) PRA in males was significantly higher than in females, and PRA tend to be decreased as age become old. 3) Normal value of PRA after double stimulation was ranged from 1.0 to 5.0 ng/ml/hr. Of total 121 hypertensive patients(55 males and 66 females), PRA was low in 33 cases(27.3%), normal in 77 cases (63.6%), and high in 11 cases(9.1%). 4) Of 55 male hypertensive patients, PRA was low in 13 cases(23.6%), normal in 35 cases (63.7%), and high in 7 cases(12.7%). Of 66 female hypertensive patients,, PRA was low in 20 cases (30.3%), normal in 42 cases(63.6%), and high in 4 cases(6.1%). High renin group was observed more frequently in male hypertensive patients than in female hypertensive patients, while low renin group more frequently in famale than in male patients. 5) Low renin group was observed more frequently in older age group than in younger age group, while high renin group more frequently in younger age than in older age group.