The neuromuscular and cardiovascular effects of vecuronium (Norcuron, Organon Teknika) were studied in 58 infants (1 day-10 months) and 65 children (1-6 years) anaesthetized either with halothane or under balanced anaesthesia. After a bolus dose of 70 micrograms/kg vecuronium the time course of neuromuscular blockade was determined using an electromyographic equipment. Onset time (time to maximal effect) was significantly shorter in infants compared with children; 1.4 +/- 0.7 min (min +/- SD) and 2.7 +/- 0.8 min, respectively. In contrast the recovery index (time for 25% to 75% recovery) was longer in infants than in children 18 +/- 6.7 min and 10 +/- 2.3 min, respectively. Repetitive administration of vecuronium, up to five maintenance doses, did not show any cumulative effects in children under balanced anaesthesia. After repetitive administration the recovery index was 12 +/- 1.7 min. Vecuronium (a bolus dose of 80 or 100 micrograms/kg) did not cause any significant change of blood pressure in infants and children anaesthetized either with halothane or by balanced anaesthesia. Infants under balanced anaesthesia showed a significant decrease in heart rate 15 min after administration of vecuronium. In contrast an increase in heart rate could be observed in children under halothane anesthesia, which was not attributed to vecuronium.