Fourteen male patients (mean age +/- SD, 52 +/- 11 years) with a history of hypertension (systolic blood pressure, 148 +/- 10 mm Hg; diastolic blood pressure, 99 +/- 2 mm Hg) were enrolled in a cross-over trial of prazosin and atenolol, with a minimum of eight weeks of treatment with each drug. Measures of lipoprotein metabolism included levels of: total plasma cholesterol, triglycerides, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, and high-density lipoprotein2 cholesterol. Lipoprotein mass was measured by analytical ultracentrifugation in low-density to very low-density lipoprotein flotation rate intervals of 0 to 12, 12 to 20, and 20 to 400, and high-density lipoprotein flotation rate intervals of 0 to 3.5 and 3.5 to 9.0. Apolipoproteins A1 and B, postheparin lipoprotein and hepatic lipase activities, and magnitude of postprandial lipemia also were determined. Mass of intermediate-density lipoproteins (flotation rate, 12 to 20) was significantly lower (p = 0.05) following prazosin therapy compared with atenolol therapy. Other lipid parameters, including triglycerides and low- and high-density lipoprotein cholesterol, were not significantly different for the two drug treatments.