The hemodynamic effects of intravenous injection of 1 mg/kg of labetalol were measured in eight healthy volunteers, using impedance cardiography and systolic time intervals. The mean systolic blood pressure was reduced by 10% (p less than 0.01) and diastolic by 6% (p less than 0.05) 30 min after the injection, and they had returned to pre-drug level 2 h after administration. Heart rate declined consistently throughout the observation period. Cardiac index was reduced by 16% (p less than 0.05), but the changes in stroke volume (- 6%) and peripheral resistance (+ 23%) were not statistically significant. Left ventricular ejection time index increased by 2% (p less than 0.05), and nonsignificant changes were found for pre-ejection period index (- 3%), total electromechanical time index (+ 1%), and PEP/LVET ratio (+ 5%). In healthy subjects resting supine the intravenous dose of 1 mg/kg of labetalol had predominantly beta-blocking effects.