A total of 555 hypertensive patients took part in a 2-year multicenter, open-label study to determine the efficacy, tolerance, and safety of long-term therapy with ramipril. In the beginning, all patients were to receive 5 mg of ramipril/day. The dosage was then adjusted in accordance with response to treatment and ranged from 1.25-20 mg of ramipril daily. Of these patients, 129 also received 25 mg of hydrochlorothiazide daily at some point during the trial. To evaluate whether tolerance to ramipril developed during long-term treatment, a subgroup of 202 patients was analyzed for efficacy maintenance. Prior to enrolling in the 2-year study, these patients had received ramipril monotherapy in a short-term, double-blind study and had been classified as responders, i.e., their diastolic blood pressure had been maintained at less than or equal to 90 mm Hg. At the end of 104 weeks of treatment, 45.9% of patients were on 2.5 mg of ramipril alone and 43.6% were on 5 mg of ramipril alone. Only four patients required the addition of 25 mg of hydrochlorothiazide. No clinically important changes occurred, and kidney function was well maintained. The most frequently reported adverse events excluding intercurrent illnesses were dizziness/vertigo (6%), asthenia (4%), nausea (3%), headache (2%), and abdominal pain, gastrointestinal disorder, rash, and increased cough (1% each). Ramipril was safe, effective, and well tolerated in the long-term treatment of patients with mild-to-moderate essential hypertension.