The study was undertaken to examine the myoplegic, hemodynamic, and histamine-releasing effects of the new aminosteroidal myorelaxant Rocuronium (esmerone, Organon firm) used to maintain anesthesia in cardiac surgical patients by orienting to early tracheal extubation. Twenty two patients aged 50 +/- 3 years operated on under extracorporeal circulation were examined. At the initial stage of maintenance, the agent in a dose of 0.6 mg/kg failed to affect cardiac pump function and to elevate plasma histamine levels. A moderate vagolytic effect was shown in 45% of cases. The incidence of myoplegia reduced in patients with significant circulatory insufficiency. In the preperfusion period, Rocuronium in a dose of 10.2 +/- 0.9 micrograms/kg/min blocked neuromuscular conduction (NMC) at a level of 5.1 +/- 1.8 to 19.2 +/- 3.5%. During hypothermic extracorporeal circulation and postperfusion period, the dosage of the myorelaxant substantially decreased. After termination of Rocuronium infusion, the time of up to 95%-recovery of NMC was 63 +/- 6 min. Early tracheal extubation was conducted in 68% of the patients 69 +/- 7.6 min after the end of the operation. Residual myoplegia was absent. The predictable recovery of NMC following the use of Rocuronium creates conditions for early activation of patients operated on under extracorporeal circulation.