Objectives. This study was designed to determine the effects of intravenous angiotensin II infusions and the short-term effects of enalaprint on venous plasma norepinephrine and norepinephrine spillover in patients with stable chronic congestive heart failure. Background. Angiotensin II has been shown experimentally to stimulate norepinephrine release. Such effects, if present in humans with congestive heart failure, could be of pathophysiologic and pharmacologic importance. Methods. In study 1,60-min angiotensin II (5 ng/kg per min) infusions were administered in eight patients with chronic New York Heart Association functional class II and III congestive heart failure. Heart rate, arterial pressure, forearm venous plasma norepinephrine, norepinephrine clearance (estimated from the clearance of tritiated norepinephrine) and norepinephrine spillover were measured after 30 min in the supine position and after 15 min each of head-up and head-down tilt. All patients were studied in a double-blind manner on two occasions with vehicle control infusions. In study 2,14 patients comparable to those in the first study had similar measurements made in the supine position before and 30 and 60 min after the administration of enalaprilat (i mg intravenously). Eight patients received a double-blind vehicle control. Results. In study 1, there were no effects of angiotensin II on heart rate, plasma norepinephrine, norepinephrine clearance or norepinephrine spillover compared with the vehicle control when the patient was in the sapine position. Mean arterial pressure increased from 85 ± 13 to 95 ± 10 mm Hg with angiotensin II. During upright tilt, plasma norepinephrine and norepinephrine spillover increased comparably with angiotensin II and the vehicle control, During head-down tilt, plasma norepinephrine decreased with both angiotensin II and the vehicle control. Norepinephrine spillover remained elevated relative to control values on both study days during head-down tilt. In study 2, both enalaprilat and vehicle coatrol administration were associated with a slight decrease in mean arterial pressure (5 ± 2 vs. 3 ± 4 mm Hg, p = NS), out bo changes were seen in plasma norepinephrine. Norepinephrine clearance and spillover decreased comparably with time after both enalaprilat and vehicle control. Conclusions. Neither the infusion of angiotensin II nor the acute administration of enalaprilat significantly alters the activity of the sympathetic nervous system as reflected by plasma norepinephrine or systemic venous norepinephrine spillover in patients with chronic congestive heart failure. These data weaken the hypothesis that angiotensin II is an important regulator of sympathetic activity in congestive heart failure.