To evaluate the possible pathophysiologic role of renin in acute renal failure observed in Korean hemorrhagic fever (KHF), the author measured the basal plasma renin activity (PRA) and the stimulated PRA by radioimmunoassay for angiotensin I in 15 normal controls and 42 KHF patients who are admitted in Seoul National University Hospital and Nation Army Hospital from Jan. 1975 to Jan. 1976. The results obtained were as follows: The mean basal PRA in normal control group was $2.9{pm}2.16ng/ml/hr$ in the patients during the oliguric phase of KHF, the mean basal PRA was $4.7{pm}2.13ng/ml/hr$, and there was statistically significant increase compared to the normal control. In the patients during the diuretic phase of KHF, the mean basal PRA was $3.4{pm}2.09ng/ml/hr$, and there was statistically significant decrease compared to the oliguric phase of KHF. In normal control group, the mean basal PRA was $2.9{pm}2.16ng/ml/hr$. And the PRA 1 hour after the administration of $Lasix^{(R)}$ 40 mg intravenously(stmulated PRA) was $5.3{pm}2.20ng/ml/hr$ and there was statistically significant increasec ompared to basal level. In oliguric phase of KHF, the mean basal PRA was $4.6{pm}2.01ng/ml/hr$. And stimulated PRA was $4.4{pm}2.34ng/ml/hr$ and there was no significant changes. In diuretic phase of KHF, the mean basal PRA was $3.3{pm}1.86ng/ml/hr$. And stimulated PRA was 5.2{pm}2.58ng/ml/hr and there was statistically significant increase compared to basal level. There were statistically no significant correlations between basal PRA and stimulated PRA and serum creatinine, BUN, urine volume and peritonial dialysis.