Pancuronium 5 ug/kg, d-Tubocurarine 50 ug/kg and the combination of pancuronium and d-Tubocurarine were given to the rabbits of same genus under intravenous urethane anesthesia to determine the neuromuscular blocking effect of each drug. The rabbit was firmly fixed to a specially constructed metal board. The sciatic nerve was stimulated by means of train of four stimulation (4 volt, 6 msec, and 2 Hz). The evoked twitch and tracing of muscle of lower extremity was recorded contineously on a physiograph. When rabbit was stable, the drug for each group was given. The results are summarized as follows: 1) The pancuronium-d-Tubocurarine combination was significantly more potent for relaxation(p<0.005) than the effect of each of the individual drugs given alone. 2) The significant muscle relaxation of pancuronium-d-Tubocurarine combination appeared at 1 minute and most potent relaxation was observed 10 minutes after drug administration and at 25 minutes, 93% of this relaxation of pancuronium-d-Tubocurarine combination was recovered. 3) Blood pressure and pulse rate after pancuronium-d-Tubocurarine combination were not changed, but the respiration was depressed at 1 minute and the most significant depression was observed at 10 minutes after drug administration. The duration of the depression lasted about 30 minutes.