This experimental study was conducted in order to observe the change 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. In clinical practice a serious sciatic nerve injury may result from an erroneous 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. Thirty-six normal adult rabbits were divided into four groups depending on injected materials and also divided into two groups of simplex exposure and closure of the nerve and of simple puncture of the exposed nerve with injection needle. The drugs were injected into the right sciatic nerve intraneurally and around the left sciatic nerve perineurally. For the functional study in the nerve, needle electrode was inserted into the calf muscle which was a pick-up muscle, and nerve potential was recorded on an electromyography(EMG) and motor nerve conduction velocity(M.N.C.V.) was also measured in the calf muscle at interval of 3, 7, 10 and 14 days after the injection. In normal control group, electrical activity on EMG was silent in resting state of the muscle and was normal motor unit action potential(normal motor unit) in volition state by demonstrating biphasic or triphasic wave patterns. Distal latency average 1.1 msec and amplitude of action potential was average 6.4 mV. The experimental groups of simple exposure and closure of the nerve and of simple puncture of the exposed nerve with injection needle showed identical EMG findings with those in normal control group. In EMG findings of both groups of normal saline and Chloromycetin injections, there were no significant differences in comparison with those in normal control group. No abnormal E.M.G. findings were observed in the left side where the drugs were injected around the sciatic nerve perineurally. Abnormal EMG findings were observed in both Penicillin and Rheumapyrine injection groups, which showed fibrillation potential and positive sharp wave in resting state and decreased amplitude or reduced numbers of normal motor unit in volition state, along with delayed M.N.C.V. Two of five cases with Penicillin injection showed denervation potentials and delayed M.N.C.N. 10 days after the injection, while all cases with Rheumapyrine injection started to demonstrate the denervation patterns on EMG and delayed M.N.C.V. 3 days after the injection, and these abnormal findings were become more evident and severe to be partial or complete denervation as the time elapsed following the injection. It was postulated that functional and physiological disabilities recorded on E.M.G. were developed after the injection only when there was a severe degree of nerve damages on the basis of histopathological study.