Nebivolol is distinct among beta-blockers by its ability to increase nitric oxide (NO) bioactivity. The contribution of this effect to the pharmacological actions of the drug, however, is difficult to ascertain in normal subjects because of the confounding contribution of the autonomic nervous system. Autonomic failure patients provide a unique model of hypertension devoid of autonomic modulation but sensitive to NO mechanisms. We propose to determine the effect of nebivolol on blood pressure in this patient population. A decrease in blood pressure will imply increased bioactivity of NO. Comparisons will be made with placebo, metoprolol (as a negative control) and sildenafil (as a positive control).