Since the Plasma-Renin Activity (PRA) value varies by many factors such as amount of sodium in-take, diuretics and posture, the basal PRA with double stimulated PRA measurement is most widely used. However the method of the study is different according to investigators and especially the PRA study in out-patient is not easy. Author attempted to establish an easy and reliable method of PRA study in out-patient and their data were compaired with those of in-patient by the study of 38 normal cases in 207 hypertensive patients. Twenty four hours urine and overnight urine sodium measurement showed that the overnight urine sodium was about 45% of that of twenty four hour urine. More than 70mEq of overnight urine sodium is considered to be borderline to neglect sodium intake for study. The PRA of normal adult was measured at 30 minutes and one hour rest in supine or sitting position after arrival to hospital. There were minor increase of PRA after 30 minutes and one hour rest than basal PRA which will not confuse the evaluation of PRA. After Lasix 40mg and 20mg intravenous injection with walking respectively, the PRA changes were measured in 30 minutes, 1, 2, and 3 hours in normal adult. The results appeared that Lasix 20mg intravenous injection and 1 hour walking double stimulation is suitable method of PRA stimulation test in out-patient clinic. The Lasix 40mg I.V. and 2 hour walking stimulation test is considered to be suitable method of PRA stimulation test in ward patient. With above study, the following method of PRA study in out-patient clinic is recommended; 1) Overnight fasting and overnight urine collection for urinary sodium measurement 2) Patient should visit hospital in fasting state and take rest for 30 minutes in supine or sitting position and thereafter take blood sample about 5-10ml as out-patient basal PRA. Inject Lasix 20mg intravenously and walk for 1 hour and take blood sample again as double stimulation test. As double stimulation test of PRA for in-patient, Lasix 40mg l.V. and 2 hours walking is recommended. By using above method, the basal PRA in clinic in 16 young normal adults was 2.30+/-1.02(0.70-3.47)ng/ml/h sitting rest and 1.76+/-1.21(0.1-4.03)ng/ml/h in supine rest. In 47 non-hypertensive ward patients who will not have any abnormality in PRA, the 24 hour urinary sodium was average 221mEq and the basal PRA was and the basal PRA was 1.46+/-0.89(0.30-3.75)ng/ml/h. In outpatients with essential hypertension without complication, the average basal PRA was not different from that of normal adult. However male ward-patients with essential hypertension without complication had slightly higher average PRA than normal adult. The distribution of low(<0.56ng/ml/h) average(0.57-2.35ng/ml/h) and high(>2.36ng/ml/h) renin groups in essental hypertension showed higher incidence of high renin group in male ward-patients. But in out-patients with hypertension, the low renin group of patient was high. Relatively low normal value of PRA in this study may be due to high sodium in-take. The higher incidence of high PRA group in essential hypertension of in-patients may be due to the difference of hypertensive status between out-patient and in-patient.