To determine the onset time, duration of action and recovery time of high-dose vecuronium, 70 patients were assigned to receive either 100, 150, 200 or 300 micrograms.kg-1 of vecuronium for muscle relaxation during elective surgery. Neuromuscular blockade was continuously quantitated by recording the EMG response to stimulation of the ulnar nerve. The onset time from the time of vecuronium administration to maximum blockade decreased from 4.6 +/- 1.1 to 2.4 +/- 0.5 min when the vecuronium doses increased from 100 to 300 micrograms.kg-1. Significant differences were observed in the onset time between the 100 micrograms.kg-1 dose and the other dose groups. Endotracheal intubating conditions were excellent in all patients except 3 in the 100 micrograms.kg-1 dose group. The duration of action from the time of injection to 25% recovery increased from 32 +/- 9 to 138 +/- 48 min in a dose dependent manner. The duration of action after increment doses of 40 or 50 micrograms.kg-1 up to 25% recovery of T1 did not vary significantly within the same dose group. With an initial dose of 150 micrograms.kg-1 and subsequent increment doses of 50 micrograms.kg-1 or less, the duration of action remained constant. The recovery time from 25 to 75% recovery was within 11 minutes when antagonists were administered. High-dose vecuronium may, therefore, be a useful alternative to SCC, when a rapid onset is required and to pancuronium, when a rapid recovery from neuromuscular blockade is requested.