Carvedilol (BM 14190) is a new compound with combined nonselective beta-adrenoceptor blocking activity, devoid of ISA, and a precapillary vasodilating effect. Its acute haemodynamic effects were studied by invasive techniques in 10 patients given 25 mg carvedilol and noninvasively in 10 patients given 25 mg and in 10 given 50 mg orally. All had essential hypertension. In the invasive study intraarterial blood pressure was measured and cardiac output was determined by the dye-dilution method using Cardio-Green as the indicator. Peripheral haemodynamics in all 30 patients were studied in the forearm using strain gauge plethysmography. Measurements were made at rest before and repeatedly for 90 minutes after oral administration of one capsule of 25 mg or 50 mg carvedilol. Significant reductions in the systolic and diastolic blood pressures (p<0.05–0.001) were observed in all groups. Cardiac output showed a small, non-significant decrease from 5.8 l/min to 5.1 l/min. Total peripheral resistance did not change, whereas resistance in the forearm fell by 16% (p<0.05). These findings are different from what would have been expected acutely after administration of a pure beta-adrenoceptor blocking agent. They indicate that carvedilol possesses vasodilating activity in addition to its beta-adrenoceptor blocking effect.