The effects of propranolol and prazosin on plasma lipoproteins in patients with essential hypertension were evaluated according to a crossover protocol of two 8-week periods with a washout of 4 to 6 weeks. Eleven patients with moderate hypertension (greater than 90 but less than or equal to 144 mm Hg, diastolic) and slightly overweight (+10% to +/- +30%, according to Metropolitan Life Insurance tables) were selected. No dietary changes were prescribed. Plasma cholesterol, triglycerides (TG), and lipoprotein changes were monitored at the beginning of each sequence and at 2-, 4- and 8-week intervals. Prazosin, when given first, did not essentially modify any of the metabolic parameters, except for a slight elevation in plasma apoprotein AI levels, i.e., the main protein component of high density lipoprotein (HDL); propranolol caused a significant rise in total TG and very low density lipoprotein TG (VLDL-TG) levels (+37.3% and +23.9%, respectively). Somewhat lower total TG (+19.6%) and vLDL (17.8%) TG elevations were noted when propranolol was given first; plasma glucose was also significantly raised (+12.8%). Triglyceride and glucose levels returned to normal upon changing to prazosin. Total plasma- and lipoprotein-associated cholesterol levels were essentially unchanged with either drug; similarly, no significant changes were detected in total plasma apoprotein B (the main protein component of LDL and also VLDL), a component of apoprotein AI levels. Uric acid levels were slightly raised on propranolol. There was an 8.8% reduction in uric acid levels when the medication changed from propranolol to prazosin.