A randomized, double-blind, parallel treatment trial was carried out in 24 patients with moderate to severe hypertension to compare the effectiveness and tolerance of two treatment regimens in reducing and maintaining supine diastolic blood pressure below 90 mmHg. Patients in Group I received 10 to 40 mg enalapril maleate per day with the addition of 50 mg hydrochlorothiazide per day and then 250 to 1000 mg alpha-methyldopa per day, if necessary. Patients in Group II received 50 mg hydrochlorothiazide per day with the addition of 80 to 240 mg propranolol and then 100 to 200 mg hydralazine per day, if necessary. Apart from the hydrochlorothiazide dosage which was fixed, the dosage of the other active drugs was titrated incrementally until the target blood pressure level was achieved. Blood pressures, heart rate and body weight were monitored at 2-weekly intervals during 26 weeks of active therapy. In Group I, blood pressure control was achieved and maintained with enalapril alone in 9 patients, 2 patients required double therapy and 1 patient triple therapy. In Group II, 9 patients required double therapy, 2 triple therapy, and only 1 patient received monotherapy. Supine and erect blood pressure control was comparable in both groups. There was, however, a significant decrease in supine heart rate in patients in Group II. More importantly, 8 of the 12 patients in Group II experienced non-life threatening adverse reactions (4 were hypokalaemic and required supplementary potassium, 2 had cold hands and feet, 1 man had sexual dysfunction and 1 acute gout) and no adverse reactions were reported by Group I patients.