The systemic and renal hemodyanmic effects of bupicomide were studied in 10 male patients with uncomplicated essential hypertension of moderate severity. Bupicomide significantly reduced systolic, diastolic, and mean arterial pressure and peripheral vascular resistance and this hypotensive effect was associated with a reflexive increase in heart rate, left ventricular ejection rate, and cardiac index; it had no effect upon other reflexive sympathetic adjustments induced by upright tilt and the Valsalva maneuver. Bupicomide also increased renal blood flow and decreased renal vascular resistance, but it had no effect upon the glomerular filtration rate. The hypotensive mechanism of bupicomide therefore is mediated by peripheral arteriolar dilation, through vascular smooth muscle relaxation. The more immediate clinical side effects of bupicomide are related to its strong vasodialting action and include headaches, cutaneous flushing, and tachycardia.