This placebo-controlled, double-blind, multicenter study examined the efficacy, safety, and tolerability of the angiotensin-converting enzyme inhibitor, moexipril, in lowering blood pressure in mildly to moderately hypertensive patients. Patients were initially randomized into four groups, two of which received moexipril 7.5 mg per day and two received moexipril 15 mg per day, for first 12 weeks of treatment. Patients then entered a withdrawal phase with one of the groups in each dose category continuing that dose of moexipril and one receiving placebo for 12 more weeks. From 223 patients randomized initially, 190 completed the 12-week withdrawal phase. In the two dosage groups from baseline to 12 weeks, sitting diastolic blood pressure decreased from 101.1 to 92.8 mm Hg for the 7.5-mg group and from 100.7 to 91.3 mm Hg for the 15-mg group (p < 0.05 baseline to week 12 in both groups) with a significant difference between those groups attained at week 12 only (p = 0.03). By the end of the withdrawal phase (24-week evaluation), the group that continued to receive 7.5 mg moexipril decreased diastolic blood pressure by 8.2 mm Hg, whereas the corresponding placebo group decreased diastolic blood pressure by 3.7 mm Hg. Although the difference between these two groups was not significant at the 24-week end point, all other time points differed significantly between groups at p less-than-or-equal 0.017. Similarly, whereas the corresponding placebo group had a mean reduction in diastolic blood pressure of 4.6 mm Hg, the group that continued 15 mg of moexipril showed a mean diastolic blood pressure reduction of 10.6 mm Hg (p < 0.001 between groups). No comparison between the two moexipril dosage groups was significant, however, during the withdrawal phase. These results during medication withdrawal indicate that moexipril is effective in significantly lowering diastolic blood pressure.