The antihypertensive effect of labetalol was evaluated in 18 adult black patients with mild to moderate essential hypertension previously controlled with a combination of a diuretic and a beta blocker. After a 4-week washout period, standing blood pressure had increased from 138 +/- 2.2/85 +/- 1.5 mmHg, (mean +/- SEM) to 154 +/- 1.9/100 +/- 0.6 mmHg. Labetalol was then titrated to a maximum of 600 mg BID to obtain a standing diastolic blood pressure of less than or equal to 90 mmHg and/or a decrease of greater than or equal to 10 mmHg from baseline (end of washout period). By the end of the labetalol titration period, standing blood pressure had decreased to 140 +/- 2.0/84 +/- 1.5 (p less than 0.01). Following a 2-week maintenance period, standing blood pressure was 136 +/- 1.6/80 +/- 1.5 mmHg (NS vs. titration). Labetalol therapy was well tolerated and reduced diastolic blood pressure to less than or equal to 90 mmHg in 17 of 18 patients, 13 of whom required dosages less than or equal to 300 mg BID. The average reduction in standing heart rate while on labetalol was 4 bpm (p less than 0.01). Side effects were limited to skin rash in one patient and possible mild urinary retention in another. These data indicate that labetalol is an effective antihypertensive for black patients with mild to moderate essential hypertension.