BACKGROUND: Rapid-sequence intubation is a common technique to reduce anesthetic complication. Due to side effects of succinylcholine, nondepolarizing muscle relaxants have been tried. Rocuronium is a new nondepolarizing muscle relaxant with a brief onset of action, but devoid of the adverse reaction associated with succinylcholine. Most local anesthetics decrease neuromuscular transmission and pontentiate neuromuscular blocks of muscle relaxants. The purpose of this study was to examine the effect of lidocaine on the onset time of rocuronium-induced neuromuscular blockade in adults. METHODS: Fourty five patients, ASA physical status I or II, were randomly divided into three groups. Anesthetic induction with thiopental 5 mg/kg was made. Succinylcholine (1.0 mg/kg) was administered intravenously in group 1. Rocuronium (0.6 mg/kg) was given in group 2, additional lidocaine (1.0 mg/kg) was given intravenously 1 minute prior to the administration of rocuronium in group 3. Neuromuscular blockade was assessed by train-of-four at the adductor pollicis muscle with supramaximal stimulation of the ulnar nerve (2 Hz, 0.2 msec) every 10 seconds. The condition of intubation, the appearance of arrhythmias, side effects of drugs, and the changes of mean arterial pressure and heart rate were checked and compared in peri-induction periods. RESULTS: The onset time of group 1 (55.1 14.9 sec) was faster than that of group 2 (137.8 46.0 sec) and group 3 (139.3 41.0 sec), but there was no difference between the onset time of group 2 and that of group 3. Intubating conditions were good or excellent in all groups, but group 1 and 3 were better than group 2. There was no difference between the three groups in hemodynamics. More adverse effects were observed in group 1, that of group 2 and 3 were observed in only one case. CONCLUSIONS: The authors concluded that lidocaine is not effective on the onset time of rocuronium, but improves the intubating condition. Rocuronium is devoid of side effects of succinylcholine, but not a alternative to succinylcholine because its onset time is too slow when compared with succinylcholine.