The effect on plasma lipids of a new beta-blocker bucindolol, which possesses weak alpha-adrenergic blocking property and intrinsic sympathomimetic activity, given orally over a 3-month period as a monotherapy or with a thiazide diuretic to 44 patients with essential hypertension was studied. The mean level of plasma HDL cholesterol concentration increased significantly during 3 months monotherapy with bucindolol or with bucindolol and diuretic. This increase was due to the increase of HDL3 subfraction. There were no significant changes in the concentrations of plasma triglycerides or total cholesterol during treatment. The ratio of HDL cholesterol to total cholesterol increased significantly. The concentration of apoprotein A-I decreased significantly in both treatment groups, but the level of apoprotein B remained constant among treatment groups. The results support the earlier observations that beta-adrenergic blocking agents with different pharmacologic properties differ as regard to their effects on plasma lipids and lipoproteins.