Comflicting results have been reported on whether ketamine potentiates the neuromuscular effect of succinylcholine or other non-depolarizing agents. Notably, there has been no reported clinical evatuation of the influence of ketamine upon the neuromuscular action of vecuronium a new muscle relaxant. The present study was undertaken to estimate the influence of ketamine upon the neuromuscular action of vecuronium with a single bolus injection of ED95. Forty-five ASA class l or ll surgical patients were divided into three groups: l, ll and lll and were given thiopental sodium(5mg/kg), ketamine 3mg/kg and ketamine 5mg/kg as induction agents, respectively. The duration and recovery index of group ll and lll (35.20±2.30 and 16.20±1.37 min., 52.60±3.98 and 25.47±3.78min., respectively) were longer than those in group l (24.87±1.59 and 10.66 ± 1.23 min.). But group l had a lower TOF ratio(27.40±3.09%) at 75% single twitch recovery than group ll and lll (41.87±3.25 and 45.27±3.67%, respectively). The increase in duration and the recovery index of group lll were greater than that of group ll. It was concluded that ketamine woudly potentiate the neuromuscular action of vecuronium in a dose-dependent manner. We suggest that combination of ketamine and vecuronium requires careful postoperative neuromuscular monitoring for the recovery from a vecuronium induced neuromuscular block.