The changes in EMG evoked by train-of-four (TOF) stimulation of ulnar nerve were recorded to determine proper single bolus dose of vecuronium for endotracheal intubation in surgical patients. Onset and duration of neuromuscular block were judged by percent depression of EMG. Mean time intervals for 90% depression in TOF seen in 0.10 mg.kg-1 vecuronium group (n = 10), 0.15 mg.kg-1 vecuronium group (n = 10) and 0.20 mg.kg-1 vecuronium group (n = 10), were 181.1 sec, 135.0 sec and 120.0 sec, respectively. Similarly, mean time intervals for 100% depression for each vecuronium group were 240.0 sec, 177.5 sec and 160.0 sec, respectively. Onset time intervals in both 0.15 mg.kg-1 and 0.20 mg.kg-1 groups were significantly shorter than that in 0.10 mg.kg-1 group (P less than 0.05). On the other hand, mean time intervals for 25% recovery in EMG were 53.6 min in 0.10 mg.kg-1 group, 63.3 min in 0.15 mg.kg-1 group and 104.3 min in 0.20 mg.kg-1 group. No statistically significant difference was observed in recovery time between 0.10 mg.kg-1 and 0.15 mg.kg-1 group. These results indicate that the appropriate dose of vecuronium for rapid intubation is considered to be 0.15 mg.kg-1. This dose is allowable for surgical procedures of short duration.