A multicentre randomised double-blind trial was performed in order to compare the therapeutic efficacy and acceptability of the angiotensin converting enzyme (ACE) inhibitor perindopril with those of atenolol in mild to moderate hypertension. After one month of placebo, 173 patients with supine diastolic blood pressure (DBP) between 95 and 125 mmHg were randomised to receive perindopril 4 mg once daily or atenolol 50 mg once daily. Monthly assessments were made for three months. Treatment was adjusted at these visits if supine DBP was greater than 90 mmHg; the dose was first doubled (8 mg perindopril or 100 mg atenolol once daily) and then hydrochlorothiazide was added. The pretreatment blood pressure levels were similar in both groups. Supine DBP was 105.5 +/- 0.9 mmHg (n = 85) in the perindopril group and 106.9 +/- 0.9 mmHg (n = 88) in the atenolol group. At the end of the third month, the study target blood pressure (supine DBP less than or equal to 90 mmHg) was achieved in a significantly (P = 0.006) larger percentage of patients in the perindopril group (78%) than in the atenolol group (58%). This appeared to be due to a greater potentiation of the antihypertensive effect by the addition of diuretic to perindopril than to atenolol. The fall in systolic blood pressure was significantly greater in the perindopril group than in the atenolol group (supine: 26.5 +/- 2.0 mmHg vs. 20.6 +/- 2.0 mmHg; P = 0.042) although the fall in DBP was comparable (supine: perindopril 17.4 +/- 0.9 mmHg, atenolol 15.6 +/- 1.1 mmHg; P = 0.195).(ABSTRACT TRUNCATED AT 250 WORDS)