In the human isolated arm preparation applied tourniquet on the upper arm, the neuromuscular blocking effects of ketamine were confirmed with the changes of first twitch height (T1) and train of four ratio (T4R) induced from 2Hz ulnar nerve stimulation (ABM Datex Co.) at 20 minutes after administration of ketamine. The results obtained were as follows; In the control group administered of saline, T1 was elevated to 6.48% compared with before tourniquet applied but T4R was not changed through the whole of the process. In the group I administered of ketamine 1 mg/kg, T1 and T,R were depressed of 8.68% and 29.59% respectively but T1 was not significant. In the group II administered of ketamine 2 mg/kg, T1 and T4R were depressed of 43.4% and 40.4% respectively. T1 and T4R in the group I and II were significantly depressed comparing with control group.