Patients treated with beta-blocking agents often complain of fatigue during exercise. Exercise capacity is decreased under this condition. Nebivolol is a new beta 1-adrenoceptor antagonist with a particular hemodynamic profile, which might be due to an ancillary property. Five milligrams once daily seems the optimal dose for antihypertensive treatment. In a double-blind, placebo-controlled crossover study, the effects of nebivolol on maximal and endurance exercise capacity are compared with those of atenolol in healthy volunteers. The hemodynamic and metabolic effects during exercise are also studied. Nebivolol 5 mg once daily and atenolol 100 mg once daily decrease blood pressure at rest similarly. At these dosages nebivolol shows a smaller decrease in heart rate than atenolol. During exercise, the rise in systolic blood pressure and heart rate is less depressed with nebivolol than with atenolol. In contrast to atenolol, nebivolol does not decrease maximal and endurance exercise capacity, and does not increase perceived exertion significantly. Changes in hemodynamics influence maximal exercise capacity. Since nebivolol has less effect on exercise hemodynamics than atenolol, this might explain why maximal work capacity is not changed during nebivolol. During endurance exercise metabolic effects are thought to be more important. Under nebivolol glycerol and NEFA production is less depressed during exercise and might explain the preserved endurance capacity. These data suggest less beta blockade during nebivolol than during atenolol at the dosages used in this study. In conclusion, at a dose known to be antihypertensive, nebivolol does not alter exercise capacity significantly in healthy volunteers.