Twenty-seven patients with uncontrolled hypertension (diastolic blood pressure greater than or equal to 95 mm Hg) receiving thiazide diuretics were treated with the addition of either propranolol (n = 10) or prazosin (n = 17). Nine patients were successfully controlled with propranolol and 12 with prazosin. Six patients required both study drugs for optimal blood pressure control, 5 of whom had received prazosin as the initial study drug. Changes in serum lipid components and cardiac performances with the addition of the study drugs were monitored. A decrease in total cholesterol and an increase in high-density lipoprotein (HDL) cholesterol were seen when prazosin was added, and an increase in total cholesterol and a decrease in HDL cholesterol occurred after the addition of propranolol. Although in this small group of patients these changes did not reach statistical significance, they were similar to changes described in other studies in which these drugs were used as monotherapy for hypertension. The only lipid change of statistical significance was a small increase in the serum triglyceride concentration in patients receiving propranolol. The findings for total cholesterol and its fractions suggest that the effects of the study drugs may not be additive to those of thiazides and that thiazides had already effected a maximal lipid response. Both agents in combination with a thiazide diuretic were equally effective in decreasing diastolic blood pressure to the goal of less than or equal to 85 mm Hg.(ABSTRACT TRUNCATED AT 250 WORDS)