Systemic, renal and splanchnic hemodynamics and certain reflex and endocrine responses were determined in 10 patients with essential hypertension before and after intravenous administration of urapidil, a new antihypertensive agent that acts through both central and peripheral alpha-adrenergic inhibitory mechanisms. The reduction in mean arterial pressure by 12% (103 +/- 3 vs 91 +/- 6 mm Hg, p less than 0.05) was mediated through a decreased total peripheral resistance index (from 34 +/- 2 to 25 +/- 3 U/m2, p less than 0.01), which was associated with a significant reflexive increase in cardiac index, heart rate and serum norepinephrine level. This hypotensive effect was also associated with blunted Valsalva overshoot and orthostatic hypotension, suggesting peripheral arteriolar and venular dilation. Renal and splanchnic blood flows increased (p less than 0.05), resistances in these vascular beds decreased (p less than 0.01) and there were no changes in creatinine clearance or glomerular filtration fraction. Thus, intravenous urapidil reduced arterial pressure by decreasing total peripheral, renal and splanchnic resistances associated with maintained organ flows and increased heart rate and cardiac index.