Five healthy young men received, in a double-blind fashion, single oral doses of 10 mg betaxolol, 40 mg betaxolol, 50 mg atenolol, 40 mg propranolol, and placebo. After the dose each received serial 12-minute infusions of isoproterenol sulfate through the dose range 0.5 to 32 micrograms/min until the heart rate rose by 40 bpm or the subject could not tolerate the effects of the infusion. Heart rate, finger tremor, blood pressure, and forearm blood flow were measured after each infusion. Dose-response curves were constructed for the changes in these parameters with increasing doses of isoproterenol. The ascending order of potency of the drugs in preventing the changes in heart rate, finger tremor, diastolic blood pressure, forearm blood flow, and forearm vascular resistance induced by isoproterenol was placebo, 10 mg betaxolol, 50 mg atenolol, 40 mg betaxolol, and 40 mg propranolol. The ascending order of potency of the drugs in preventing the change in systolic blood pressure induced by isoproterenol was placebo, 10 mg betaxolol, 50 mg atenolol, 40 mg propranolol, and 40 mg betaxolol. Betaxolol, 10 mg, is equally cardioselective to 50 mg atenolol and at a dose of 40 mg betaxolol also exhibits cardioselectivity.