It has been suggested that plasma renin activity (PRA) and its response to volume depletion may be abnormal in that it shows little or exaggerated change in patients with chronic renal failure and hypertension. Intravenous furosemide stimulation test was performed in 46 control subjects and 51 patients with chronic renal failure and/or malignant hypertension in order to evaluate PRA response. In contrast to the consistent increase in PRA in control subjects (from 2.5¡¾1.95 to 4.5¡¾2.51 ng/m1/hr), no consistent increase was observed in patients with chronic renal failure, especially in those who showed favorable response to antihypertensive therapy (from 2.5¡¾2.21 to 2.9¡¾2.46 ng/ml/hr). But poor responder to antihypertensive treatment showed considerably higher PRA before and after furosemide stimulation (from 4.9¡¾1.96 to 6.4¡¾1.71 ng/ml/hr) than the responder group did. Moreover, this group seemed to retain the ability to increase PRA in response to intravenous furosemide stimulation. Thus it became apparent that responder group was unable to increase PRA normally in response to furosemide as well as volume depletion, while poor responder seemed to retain that ability. Thus intravenous furosemode may serve as a convenient way to differenfiate those who might be benefited by conservative antihypertensive measures from those who would require more drastic measures such as bilateral nephrectomy for their optimal blood pressure control.