Hemodynamic responses and exercise capacity were studied during maximal exercise in 25 young hypertensive persons (mean age 40 years) taking placebo, diltiazem (mean 216 mg/day) and atenolol (mean 80 mg/day). The study was a crossover, double-blind, randomized trial, each medication period lasting 2 months. Sitting blood pressure (BP) was 160 +/- 19/109 +/- 8 mm Hg after run-in. Both drugs decreased BP significantly, diltiazem by 10/ 11 mm Hg and atenolol by 16/14 mm Hg (difference not significant between drugs). During exercise there were no differences among patients taking placebo, diltiazem and atenolol in peak workload and rating of perceived exertion. Atenolol significantly attenuated the increase in heart rate, BP and heart rate-BP product at each workload. Diastolic BP during exercise was significantly lower (6 to 10 mm Hg) during diltiazem therapy than during placebo at each workload. Thus, both diltiazem and atenolol decrease rest BP significantly without impairing exercise capacity.