To determine the onset time and duration of high doses of vecuronium, 40 ASA Physical Status 1 and 2 patients were randomly assigned to receive either 100, 200, 300, or 400 micrograms/kg of vecuronium bromide for muscle relaxation during elective general surgery. Neuromuscular blockade was continuously quantitated by recording the electromyographic response to stimulation of the ulnar nerve train-of-four. The rate of onset of neuromuscular blockade, endotracheal intubating conditions, duration of neuromuscular blockade, and hemodynamic effects of vecuronium at each dose were evaluated and compared. The time from vecuronium administration to complete abolition of twitch tension (T1 = 0%) decreased from 208 +/- 41 to 106 +/- 35 s as the vecuronium dose was increased from 100 to 400 micrograms/kg (P less than 0.01). Corresponding times to endotracheal intubation (T1 less than 20%) also decreased from 183 +/- 24 to 96 +/- 31 s with increasing doses (P less than 0.01). Recovery time (T1 = 25%) increased from 37 +/- 13 to 138 +/- 24 min with increasing doses (P less than 0.01). No significant hemodynamic differences between the four groups were observed. Endotracheal intubating conditions were good or excellent in all patients. High doses of vecuronium may, therefore, be a useful alternative to succinylcholine when a rapid onset of neuromuscular blockade is required.