Most local anesthetics intravenously administered inhibit neuromuscular transmission or enhance the neuromuscular block of both nondepolarizing and depolarizing musde relaxants. Local anesthetics used to treat cardiac arrhythmias intraoperatively or postoperatively may, therefore, greatly augment a residual neuromuscular block. To obtain adequate balanced anesthesia and postoperative analgesia, general anesthesia with epidural anesthesia is frequently selected. In the present study we investigated the effects of lidocaine HC1 administered into epidural space on the neuromuscular blocking action of vecuronium. Eighty adult gynecological patients of ASA class I or II were studied. Patients were divided into four groups as follows ; Group I (n=20); vecuronium 0.1 mg/kg iv administered only Group II(n=20); vecuronium 0.1 mg/kg iv and lidocaine 6 mg/kg administered into epidural space Group III(n=20); vecuronium 0.1 mg/kg iv and lidocaine 8 mg/kg administered into epidural space Group IV(n=20); vecuronium 0.1 mg/kg iv and lidocaine 10 mg/kg administered into epidural space Patients of experimental groups II, III and IV were anesthetized by epidural block with 2 % lidocaine followed by general anesthesia 15 minutes later. Before induction with fentanyl(3 ug/kg), droperidol(0.04 mg/kg), thiopental sodium (5 mg/kg) and vecuronium(0.1 mg/kg) iv, neuromuscular monitoring was set by using ABM(Anesthesia and Brain activity Monitor, Datex Co, Finland) which stimulating ulnar nerve at the wrist with supramaximal stimuli at a frequency of 2 Hz and 20 seconds interval. The electromyographic response of hypothenar muscles was recorded. Following stabilization of the control twitch height, vecuronium(0.1 mg/kg) was intravenously injected, and tracheal intubation was performed when the first twitch height of the train of four twitch response(T1) was 5 % of the controL Anesthesia was maintained with O2 (2 L/min) and N2O (4 L/min). The time of onset of action (time from vecuronium iv to 0 % of T1), time of maximal twitch depression (time from loss of T1 to reappearance of T1), Recovery index (time from recovery of 25 % of T1 to 75 % of T1) and T4 ratios (ratio of the height of the fourth twitch to T1) at 25 %, 50 % and 75% of T1 were measured and compared among the groups. The results were as follows ; 1. The time of onset of action was 3.99±0.92 minutes in the control group and 2.94±0.89 minutes in the lidocaine 10 mg/kg administered group(P<0.05). 2. The time of maximal twitch depression was 19.055.46 minutes in the control group and 24.02±6.94, 25.33±5.84, 27.07±5.26 minutes in the lidocaine 6 mg/kg, 8 mg/kg, 10 mg/kg administered groups(P<0.05). 3. Recovery index was 14.76±5.40 minutes in the control group and 20.39±4.56, 22.36±7.98 minutes in the lidocaine 8 mg/kg, 10 mg/kg administered groups(P<0.05). 4. The lidocaine administered into epidural space has little effect on the recovery of T4 compared with that of T1(P>0.05). These results suggest that the effect of lidocaine HC1 administered into epidural space on the neuromuscular blocking action of vecuronium showed prolonged depression and recovery time, and reduced time of the onset of action with dose larger than lidocaine 8 mg/kg.