The antihypertensive effect of oral labetalol and propranolol were evaluated in 65 black and 75 white patients with mild to moderate hypertension (standing diastolic blood pressure (StDBP) of 90-115 mmHg) in a double-blind multicenter clinical trial. Following a 4-week placebo phase, labetalol (n = 70) or propranolol (n = 70) was randomly assigned. During a 5-week titration phase, labetalol could be increased from 100 mg BID to 600 mg BID to achieve a StDBP of less than 90 mmHg and a decrement of greater than or equal to 10 mmHg. Propranolol could be titrated from 40 to 240 mg BID. A 3-month maintenance phase was followed by an optional 8-month maintenance phase. Hydrochlorothiazide (HCTZ) could be added at any time during the maintenance phase. Supine and standing blood pressures were measured at each visit. Statistical analysis revealed significant (ANOVA, p less than 0.05) treatment by race effects. Therefore, the treatment groups were stratified retrospectively by race. This study demonstrated that labetalol is equally effective in white and black patients, whereas, propranolol is significantly (p less than 0.05) more effective in white than in black patients. Moreover, labetalol is significantly more effective than propranolol in lowering the standing systolic/diastolic blood pressure of black patients (p less than 0.02/p less than 0.001). These blood-pressure effects were accompanied by a significantly greater (p less than 0.04) reduction in heart rate with propranolol. Furthermore, significantly more (p less than 0.05) black patients treated with propranolol compared to those treated with labetalol required the addition of a diuretic for control of their blood pressure.