To differentiate diuretic and direct cardiocirculatory properties of furosemide for elucidation of the vasodepressor mechanisms of action of the agent in the acute treatment of hypertension, the peripheral vascular effects of intravenous furosemide (3 mg/kg) on supine blood pressure (BP) and forearm hemodynamics in 11 functionally anephric hypertensive patients (creatinine clearance less than 2 ml/min) were studied. BP was recorded by sphygmomanometer and forearm hemodynamics were measured by strain gauge plethysmography. While diastolic BP decreased only 2.7 mm Hg at 30 minutes, forearm blood flow increased 55% (p less than 0.01) mediated by decreased peripheral vascular resistance of 30% (p less than 0.01) at 15 minutes which dissipated by 30 minutes. Systolic BP, indices of venous capacity, weight, hematocrit, serum electrolytes, and plasma renin activity were unchanged. No diuresis occurred. It is concluded that the early hypotensive effect of furosemide depends upon diuresis.