The aim of this 3-month double-blind study was to assess the antihypertensive effect and acceptability of perindopril in comparison with enalapril in patients with mild to moderate essential hypertension. After a 4-week placebo run-in period, 161 patients with supine diastolic blood pressure (DBP) between 95 and 115 mmHg were randomized to receive perindopril 4 mg or enalapril 10 mg once daily. If supine DBP was higher than 90 mmHg, treatment was adjusted monthly, first by doubling the dose and then by addition of hydrochlorothiazide 12.5 mg. After 3 months of active treatment the decrease in supine and standing blood pressures was statistically significant within both groups but was not statistically different between groups. The percentage of patients (65%) who achieved supine DBP of < or = 90 mmHg in the perindopril group was not significantly different from the enalapril group (73%). Monotherapy resulted in control of supine DBP in 56% of the perindopril group and 58% of the enalapril group; the addition of hydrochlorothiazide resulted in control of supine DBP in 6% and 15% respectively. The number of withdrawals for adverse events was statistically significant between groups (0 in the perindopril group and 7 in the enalapril group, p = 0.01). During active treatment the most frequently reported complaints were headaches and cough; there was not statistically difference between groups. Changes in laboratory parameters were minor and not significantly different between the two groups except for serum glucose, potassium, and triglyceride levels. In conclusion, there was no significance between perindopril and enalapril in terms of efficacy. Clinical acceptability seems to be better in the perindopril group.(ABSTRACT TRUNCATED AT 250 WORDS)