In an eight-week, multicenter open-label study of enalapril monotherapy for mild-to-moderate essential hypertension, data for 115 of the 276 participants between the ages of 55 and 75 years (whites, n = 90; blacks, n = 25) were analyzed. These data were compared with similar data for the study subset of 92 younger patients between the ages of 21 and 45 years (whites, n = 58; blacks, n = 34). The most striking finding was the overall lack of significant differences in response between older and younger patients. There were, however, significant differences in response to therapy between the two racial groups studied. In the older group, normotension was achieved in 66% of white patients and 60% of black patients with a single daily dose of enalapril ranging from 5 to 40 mg; the group means, 13 +/- 1 mg in whites vs 22 +/- 2 mg in blacks, differed significantly (P less than 0.05). Thirty-one percent of older white patients attained normotension with a daily dosage of 5 mg, whereas only 4% of black patients in this age group did so. Only 4% of the older white patients but 24% of the older black patients reached the highest recommended daily dosage of 40 mg of enalapril. Adverse reactions occurred in 11% of the older white patients and 16% of the older black patients (a nonsignificant difference), consisting mostly of gastrointestinal discomfort, malaise, dizziness, and pruritus. There were no significant biochemical abnormalities, the only consistent change being a slight increase in mean plasma potassium from 4.34 to 4.45 mEq/L in older whites (P less than 0.05). Enalapril appeared to be generally effective and well tolerated in the management of mild-to-moderate hypertension in the older subset of patients in this study. Efficacy and tolerability data for older and younger patients were comparable.