This was a double-blind multicenter study to compare the efficacy, tolerability and effects on the quality of life with isradipine and atenolol in the treatment of essential hypertension. Of 588 patients entering the 6-week placebo run-in period, 549 were eligible for randomization to receive either isradipine or atenolol for 8 weeks. If, at the end of this period, diastolic blood pressure (DBP) remained greater than 90 mm Hg, then both agents were given in combination for a further 10 weeks. Tolerability and quality of life were assessed repeatedly during the placebo and active-treatment phases. A subgroup of 30 patients were followed by 24-h ambulatory blood pressure monitoring, and their results are now being analyzed. In another subgroup of 26 patients, maximum exercise capacity, as determined by ergometer bicycle-testing, was measured once during placebo and twice during active treatment. At the end of the 24-week study period, both isradipine and atenolol as monotherapy had produced significant decreases in blood pressure. There were no significant differences overall between the compounds in quality-of-life and side-effect profiles, although there was a relative absence of ankle edema and headache with isradipine. Furthermore, patients receiving isradipine had no change in performance on exercise testing whereas patients on atenolol had a significant decrease (p less than 0.01).