A multi-centre, randomized, double-blind, parallel group study was undertaken in order to assess efficacy and tolerability of ramipril as compared to enalapril in mild to moderate hypertension. A 4-week placebo run-in period was followed by 4 weeks of treatment with active medication (5 mg ramipril or 10 mg enalapril in a single morning dose). In patients not responding to this dosage regimen at the end of a 4-week treatment period, the dose was doubled. After 8 weeks of active medication, 3 mg daily of the diuretic piretanide was added to the treatment of patients not responding to the doubled dose. A total of 202 patients was admitted in the placebo phase from which 174 patients who had evaluable data at the end of the study were included in the efficacy analysis. Based on the definition of a 'responder' as a patient who achieved a supine diastolic blood pressure of 90 mmHg or less, 40% of those on 5 mg ramipril achieved this level within 4 weeks; in the enalapril group, the corresponding figure was 36.6%. By the end of 12 weeks of active treatment, a total of 55% of the ramipril group had responded to a daily dose of 5 to 10 mg ramipril. An additional 18% responded when 3 mg piretanide was added to the regimen. In the enalapril group, 59% responded to 10 to 20 mg enalapril. A further 17% responded to addition of piretanide to 20 mg enalapril. A total of 19 patients developed 29 adverse drug events while receiving ramipril, alone and in combination with piretanide. In the enalapril group, 24 patients developed 36 adverse events during enalapril monotherapy and combination treatment. It is concluded that ramipril and enalapril in a ratio of 1:2 have comparable antihypertensive efficacy in mild to moderate hypertension but the number of adverse reactions was slightly higher with enalapril in this study.