The intra-arterial blood pressure of 20 male patients with essential hypertension was continuously recorded during dynamic exercise. Graded exercise testing on a bicycle ergometer and a stair-climbing test were performed prior to and during treatment with oxprenolol. Acute oxprenolol therapy was associated with a reduction in heart rate but little reduction in blood pressure. Chronic treatment for 14.3 weeks with oxprenolol (mean daily dose, 344 mg) was associated with a substantial reduction of blood pressure at rest and at each level of bicycle exercise. A similar antihypertensive effect was demonstrated during stair climbing. The normal blood pressure response to exercise as assessed by the relative (percentage) increase in pressure above the pre-exercise level and the rate of increase in blood pressure (per unit of work), as well as exercise tolerance, were unchanged by chronic beta-blockade with oxprenolol.