The effects of prazosin and propranolol on total serum cholesterol concentration, low-density lipoprotein and high-density lipoprotein cholesterol fractions, and serum triglyceride concentration were compared in a crossover study in 29 patients with mild to moderate essential hypertension. All patients received polythiazide at a constant dose throughout control and drug treatment periods. Comparable blood pressure reduction was achieved with prazosin (9.3 +/- 7.1 mg per day) and propranolol (183.6 +/- 154.5 mg per day). Prazosin administration was associated with a significant reduction in the concentrations of total serum cholesterol (-5.5 percent), triglyceride (-20.0 percent), and low-density lipoprotein cholesterol (-10.1 percent). High-density lipoprotein cholesterol concentration increased (+8.0 percent) as did the ratio high-density lipoprotein: total cholesterol (+14.1 percent). No significant changes in any of the serum lipid fractions were observed during propranolol administration.