Enalapril combined with an extended-release formulation of diltiazem was evaluated in a 12-week multicenter trial of 112 patients with Stages 3-4 essential hypertension. Patients were randomized to once daily therapy with enalapril 5 mg plus diltiazem ER 120 mg or 180 mg. Dosages could be titrated and other antihypertensive agents added for blood pressure control. Efficacy was assessed with sitting blood pressures at trough (24 hours postdose). Overall, there was a decrease of -21.7/-18.4 mmHg. Patients responding to enalapril/diltiazem ER alone had a reduction of -15.0/-16.3 mmHg. Of all patients, 70% achieved a trough sitting diastolic blood pressure of < 95 mmHg. Common drug-related adverse experiences were headache, dizziness, rash, and asthenia/fatigue. This once daily fixed-combination of enalapril/diltiazem ER was generally well tolerated and effective when given alone or with other antihypertensives in Stage 3-4 hypertension.