Analysis of insertional activity is a routine part of the clinical electromyogrphic examination. It provides an information of muscle excitability but it's clinical significance has not perfectively accepted yet. This study was designed to evaluate clinical usefulness of insertional activity through quantitative analysis in the diagnostic field of pathology. Monopolar needle electrode was inserted briefly in the biceps brachii, paralumbar spinal and tibialis anterior muscles of the normal and denervated muscles. Total duration and spike duration of the insertional activity were measured 10 times in each muscle and averaged. Within spike duration we measured turns, mean amplitude, turns/amplitude, RMS, mean frequency and median frequency. The measured parameters of insertional activities were not significantly different according to the muscle in normal controls. In denervated muscles, the turns, mean amplitude, RMS, mean frequency and median frequency were decreased but turns/amplitude was increased compared to those of normal controls. But there were no difference in total duration and spike duration between normal and denervated muscles. In denervated muscles the muscle power was positively correlated with turns, mean amplitude, RMS, mean frequency and median frequency, and the grade of abnormal spontaneous activities was inversely correlated with turns, mean amplitude, RMS, mean frequency and median frequency. Therefore quantitative analysis of insertional activity could be a useful method for the diagnosis of neuromuscular disease.