In clinical practice a serious sciatic nerve injury may result from an errornous injection of commonly used antibiotics and other therapeutic or prophylactic agents into the gluteal region which can occur at any age, especially common in infants, children and small debilitated patients. Although many isolated cases and several large series of injuries have been reported, the pathogenesis, pathology and its physiology of injection injury of the peripheral nerves in man have been poorly studied. This experimental study was conducted in order to observe the changes and degree of the functional disability of the sciatic nerve following injection of various drugs such as Rheumapyrine, Chloromycetin, Penicillin and physiological normal saline solution. Fourty-three normal adult rabbits were divided into four groups depending on injected materials and also divided into two groups of acute and chronic stages. The drugs were injected into the right sciatic nerve intraneurally and around the left sciatic nerve perineurally. For the functional study in the nerve, contractability of the calf muscle was recorded on a physiograph at intervals of 1, 3, 5, 15 and 30 minutes after the injection of the drugs. Rheobase, chronaxie and strength-duration curve of both extensor and flexor muscles of fet were recorded and measured on a chronaxie meter at intervals of 1, 2, 3 and 4 weeks after the injection. The physiogram showed the greatest reduction in contractability of the muscles in Rheumapyrine, moderate reduction in Penicillin and the least reduction in Chloromycetin group. In the measurements of rheobase and chronaxie there were marked increase of values in group of Rheumapyrine injection. There was no significant differences in values among the group of Penicillin, Chloromycetin and saline injections in comparison with those in the control group. In the analysis of strength-duration curve, it showed a pattern of complete denervation in 3 cases and a pattern of partial denervation in 3 out of 8 cases with Rheumapyrine injection, and a pattern of partial denervation in 3 out of 6 cases with Penicillin and 2 out of 8 cases with Chloromycetin injection. There was no significant differences in values of rheobase, chronaxie and strength-duration curve as time elapsed following the injury. It was postulated the functional and physiological disabilities were developed after the injection when there was a severe degree of nerve damages on the basis of histopathological study.