The purpose of this study was to assess the long-term efficacy and safety of moexipril, a new angiotensin-converting enzyme inhibitor, alone or in combination with hydrochlorothiazide in patients with hypertension. The patient population consisted of 281 hypertensive men and women, 30-84 years old, with seated diastolic BP between 95 and 114 mmHg. The study was a two year multicenter (22 centers), open-label protocol of moexipril monotherapy or combination therapy (with hydrochlorothiazide). Blood pressure, pulse rate, weight, adverse side-effects and laboratory studies were assessed following moexipril dosing at 7.5, 15 or 30 mg once daily or 15-30 mg daily in combination with 12.5 mg hydrochlorothiazide if the DBP was > or = 90 mmHg. The primary measure of efficacy was change from baseline in seated DBP. Secondary outcome measures included changes in seated SBP, heart rate, laboratory parameters and subjective complaints. Following one year of therapy in 183 patients, the BP fell 13/14 mmHg among patients receiving moexipril monotherapy and 18/15 mmHg those receiving combined therapy compared with baseline (P < 0.001 for both). After two years of treatment, reductions were similar in 161 patients. Forty-four (16%) patients were prematurely withdrawn from the study because of inadequate therapeutic response and 34 (12%) secondary to adverse experiences. There were no changes in pulse rate or postural BP reductions. Four adverse side-effects occurred at a frequency exceeding 2% that were possibly or probably attributable to moexipril: fatigue (3%), headache (2%), dizziness (3%) and increased cough (5%).(ABSTRACT TRUNCATED AT 250 WORDS)