Objectives. This study sought to determine the effects of enalaprilat on reflex control of sympathetic nerve activity. Background. Angiotensin-converting enzyme inhibitors decrease mortality in patients with congestive heart failure. Their efficacy appears to be related importantly to antiadrenergic effects, the mechanism for which has not been determined. Because baroreflexes tonically inhibit sympathetic outflow, and baroreflexes are blunted in heart failure, we hypothesized that these agents reduce sympathetic activity by augmenting baroreflexes. Methods. We assessed baroreflex control of sympathetic nerve activity and heart rate in patients with congestive heart failure and in control subjects before and after enalaprilat (0.02 mg/kg body weight intravenously). Arterial baroreflexes were perturbed by bolus administration of sodium nitroprusside and phenylephrine. Cardiopulmonary baroreflexes were perturbed by lower body negative pressure and head-down tilt. Muscle sympathetic nerve activity was recorded by microneurography. Results. Enalaprilat decreased systolic blood pressure in patients with heart failure and control subjects. Sympathetic nerve activity increased in control subjects but decreased in patients with heart failure after enalaprilat despite reductions in central venous pressure in this group. Baroreflex control of sympathetic nerve activity was unchanged by enalaprilat in control subjects. In patients with heart failure, both arterial and cardiopulmonary baroreflex control of sympathetic nerve activity was enhanced by enalaprilat. Baroreflex control of heart rate was unchanged by enalaprilat in either group. Conclusions. Enalaprilat augments both arterial and cardio pulmonary baroreflex control of sympathetic activity in heart failure. These augmented inhibitory influences are associated with a reduction in sympathetic outflow and may contribute to the beneficial effects of angiotensin-converting enzyme inhibitors in heart failure.