In a double-blind 3-month study in mild-to-moderate essential hypertensive patients over 50 years of age, ketanserin, a selective S2-serotoninergic antagonist with additional alpha 1-adrenergic blocking properties, has been compared with enalapril, an angiotensin-converting enzyme inhibitor. Supine and upright blood pressures and heart rates were recorded for placebo and during active treatment (-4, -2, 0, 2, 4, 6, 8, 10, and 12 weeks). Metabolic profile (plasma glucose, creatinine, sodium, potassium, total and HDL-cholesterol, triglycerides, uric acid) was monitored during treatment with placebo and at the end of the study. Mean blood pressure was equally and significantly (p less than 0.001) lowered by both drugs from 2 weeks of treatment, whereas no changes occurred in mean heart rate or in biochemical variables. Dizziness was observed in three patients on ketanserin and in one patient on enalapril, whereas headache occurred in only one patient on enalapril. These data indicate that ketanserin is as effective and well tolerated as enalapril in hypertensive patients over 50 years of age.