The experience with three groups of antihypertensive agents in a large hypertension clinic serving a black patient population is reported. A retrospective review of clinic records was undertaken to determine the efficacy and adverse effects of the centrally acting adrenergic agonists methyldopa and clonidine, the alpha-1 antagonist prazosin, and the direct vasodilator hydralazine in patients with mild and moderate hypertension. Treatment with methyldopa, clonidine, or prazosin, usually in combination with a diuretic produced a 30 to 38 mmHg decrease in systolic blood pressure, and a 24 to 28 mmHg reduction in diastolic blood pressure. Similar declines in blood pressure levels occurred when hydralazine was used with an alpha-2 adrenergic agonist or beta-adrenoceptor blocking agent. Evidence of clinical efficacy, defined as a decrease in systolic blood pressure to below 140 mmHg and in diastolic blood pressure to below 90 mmHg, was observed in 80% or more of the patients. An 88% efficacy rate was seen with methyldopa. Effective doses of the drugs varied considerably; most patients, however, responded at a dose close to the average dose for each agent. The most serious adverse effect observed was elevation of hepatic enzyme levels in patients receiving methyldopa, which necessitated withdrawal of the drug. Two patients treated with 0.4 mg clonidine twice a day experienced "rebound" hypertension when the drug was abruptly discontinued. Overall, good clinical efficacy and patient acceptance were found with these three groups of antihypertensive agents.