In a crossover study, 12 patients with mild to moderate hypertension were given placebo, captopril (12.5 to 50 mg three times a day), and nadolol (20 to 160 mg once a day) to control the resting diastolic blood pressure to a nearly identical degree (p less than 0.0001) (106.1 +/- 4 placebo, 89.6 +/- 8 captopril, 89.8 +/- 7 nadolol). Both drugs lowered (p less than 0.0004) systolic and diastolic blood pressure at rest and during exercise. However, systolic blood pressure lowering during exercise was more pronounced (p less than 0.05) with nadolol than with captopril (difference of 6 mmHg, 16 mmHg, and 21 mmHg at 5.0, 7.0, and 9.0 metabolic equivalents (METS) respectively). Heart rate was lower (p less than 0.05) at rest and during exercise with nadolol as compared with placebo and with captopril. These data imply different mechanisms of action of the two drugs at rest and during exercise and may help in selection of drug therapy in special patient subsets.