Moexipril is a new nonpeptide angiotensin-converting enzyme (ACE) inhibitor with an intermediate duration of action. The antihypertensive efficacy and safety of moexipril as add-on therapy to nifedipine retard (20 mg b.i.d.) was compared to placebo during 8 weeks in a double-blind trial with a parallel group design. A total of 203 patients with essential hypertension and a sitting diastolic blood pressure (DBP) greater than or equal to 95 mm Hg on nifedipine alone were randomly assigned to placebo or moexipril 3.75 mg o.d., 7.5 mg o.d., or 15 mg o.d. At endpoint, the adjusted mean reductions in DBP from baseline were 6 mm Hg, 9 mm Hg (p < 0.01), and 9 mm Hg (p < 0.05) in the moexipril 3.75 mg, 7.5 mg, and 15 mg groups, respectively, compared to 5 mm Hg in the placebo group. All dosages of moexipril were well tolerated, and the overall percentages of patients who reported adverse experiences were smaller than in the placebo group. We concluded that moexipril as add-on therapy to nifedipine is well tolerated and gives additional antihypertensive effects.