Activities of the elbow flexors and extensors during the movement of the elbow flexion and extension were analyzed in six normal human volunteers by electromyography (EMG). In the flexors, the majority of the muscles showed EMG activities during both the flexion and extension phases, although patterns and amplitudes of EMG activities varied from individual to individual. The biceps brachii always became less active when the forearm was in pronation. In the extensors, increase of EMG activities was observed at the period of the maximum elbow extension in the majority of cases, while no EMG activity was shown throughout the movement in some cases. During the elbow movement except at the maximum extension, the triceps brachii was almost inactive and some of their three heads, in particular the long head, often showed no EMG activity. In contrast, the anconeus was usually active, sometimes showing strong EMG activity.