Bopindolol is a new long-acting, nonselective beta-adrenoceptor antagonist with partial agonist activity. Its acute (24 hours, 2 mg, administered orally) and long-term (3 weeks, 2 to 4 mg) hemodynamic and hormonal effects were studied in a single-blind placebo-controlled trial in 10 hypertensive subjects. The initial response (mean +/- SE) to bopindolol was a fall in cardiac output (-12% +/- 2%) and heart rate (-11% +/- 2%). Mean arterial pressure began to fall 3 to 4 hours after administration in parallel with a decrease in systemic vascular resistance, which had increased initially. Twenty-four hours after administration, mean arterial pressure and systemic vascular resistance were reduced by 12% +/- 2% and 12% +/- 5%, respectively. By that time heart rate and cardiac output did not differ from baseline values despite beta-blockade. After 3 weeks of treatment mean arterial pressure had fallen by 9% +/- 2% and renal blood flow and glomerular filtration rate were not changed. One week after withdrawal from treatment mean arterial pressure and heart rate were no longer reduced, but beta-blockade could still be demonstrated, establishing the long duration of action of the drug.