After screening a local population in the northern part of The Netherlands for hypertension, 125 patients (116 of whom had not previously used antihypertensive drugs) with a five times elevated diastolic pressure (DP) of between 95 and 130 mmHg were randomized and treated daily either with atenolol 50 mg o.d. (n = 62) or with captopril 25 mg b.i.d. (n = 63) for 2 months under double-blind conditions. During this period the DP fell by 9 mm under atenolol (from 107 +/- 8 to 98 +/- 8) and by 8 mm under captopril (from 107 +/- 7 to 99 +/- 9). The number of responders with a DP = less than 90 mmHg was 21% and 20%, respectively. After 2 months the double-blind period was ended and the patients were submitted to a medication protocol for another 4 months in which an increased dose and additional nifedipine were given to non-responders. The response rate rose to 76% (atenolol/nifedipine combination) and to 60% (captopril/nifedipine combination) - NS. It is concluded that low doses of atenolol and captopril are equally effective in lowering blood pressure in uncomplicated mild to moderate hypertension.