We report the first comparative study on enalapril maleate, a new angiotensin converting enzyme inhibitor, in patients with uncomplicated mild to moderate essential hypertension. Fifty-four patients were randomly assigned to treatment with enalapril or propranolol for 16 weeks following a placebo run-in-phase. The study was double-blind. Enalapril and propranolol both reduced blood pressure, though the changes were significantly treated with enalapril were normotensive at the end of the study. Enalapril treatment was associated with a significant reduction in weight. Both drugs raised plasma potassium and urea. No haematological abnormalities occurred with enalapril and there were no reports of rash, taste disturbance or proteinuria. At the end of the trial the mean daily dose of enalapril was 20 mg and that of propranolol was 180 mg.