It is well known that local anesthetics, which block impulses in peripheral nerve fibers have marked effects on the central nervous system. The drugs, when given in small, subconvulsive doses, produce sedation, central analgesic action, and anticonvulsive effects. When subconvulsive doses of the local anesthetic, lidocaine, was administered to animals, there was marked depression of motor activity and probably this depression was due, at least in part, to sedation(Wagman et al, 1967). Local anesthetics are administered in combination with one another to produce rapid onset and prolonged duration of anesthesia. However the combined administration of large doses of multiple durgs generally is considered an important cause of local anesthetic toxicity. Some authors have said that combined administration of local anesthetics in animals showed that systemic toxicity was additive, but others not. So, the present study was undertaken to evaluate the effect of two combined local anesthetics on the motor activity by way of the effects of combined 2 local anesthetics on the central nervous system. As experimental animals, 460 mice, weighing about 20gm, were used. Subconvulsive doses of lidocaine 25mg/kg, 50 mg/kg, tetracaine 7.5mg/kg, 15 mg/kg, lidocaine 25mg/kg combined with tetracaine 7.5mg/kg and lidocaine 25mg/kg combined with bupivacaine 7.5mg/kg were administered. The motor activity was measured with a "Selective Activity Meter". The results are summarized as follows: 1) The group of mice treated with lidocaine showed markedly inhibited motor activity in comparison with the control group and the inhibitory action of lidocaine 25mg/kg and 50mg/kg was similar. 2) In the group treated with tetracaine there was marked inhibition of motor activity throughout the experiment and the inhibitory action of tetracaine 15mg/kg was more marked than 7.5mg/kg. The group treated with lidocaine 25mg/kg was more inhibited than the group with tetracaine 7.5mg/kg and less inhibited than the group with bupivacaine 7.5mg/kg. 3) In the group treated with bupivacaine there was strong inhibition of motor activity throughout the experiment and the inhibitory action of the group with bupivacaine 7.5mg/kg was less than the group with bupivacaine 15mg/kg. Inhibition in the group treated with bupivacaine 7.5mg/kg was shown to be more intense than any of the other drugs used in this test. The group treated with tetracaine 15mg/kg was more inhibited than the group with lidocaine 50mg/kg and less inhibited than the group with bupivacaine 15mg/kg. 4) The group treated with a combination of lidocaine 25mg/kg and tetracaine 7.5mg/kg was more inhibited in comparison with control and each treated group, but this increase of inhibition over each treated group was small. 5) The group treated with a combination of lidocaine 25mg/kg and bupivacaine 7.5mg/kg was more inhibited than the control and each treated group, but the increase of inhibition over each treated group was small. From the results described above, it may be concluded that local anesthetics depress the central nervous system and bupivacaine depresses the central nervous system more than lidocaine and tetracaine. Combined treatment does not show a synergistic effect on the motor activity.