In this work, the electromyographic (EMG) activity of the flexor and extensor carpi ulnaris muscles was studied in flexion movements of the forearm in the semipronation, supination and pronation positions with 50% maximum voluntary contraction. Ten untrained volunteers, (5M, 5F), 21 to 38 years old, were enrolled and requested to perform three serial movements in a double-pulley apparatus. The EMG signals were acquired with differential surface electrodes and digitalized by a 12 bit A/D converter board, using the AqDados software which provided numerical data as root mean square values. The results showed that both muscles were active in the conditions studied, independent of the forearm position. The flexor carpi ulnaris muscle was relatively less active than the extensor carpi ulnaris muscle in the semipronation position, but relatively more active in the supination position; both muscles showed similar activity in the pronation position. There were significant differences in the electromyographic activity among the semipronation, supination and pronation positions in both the flexor and extensor carpi ulnaris muscles, with the highest values obtained in the pronation position and the lowest in the supination position. However, there were no significant differences between the values obtained for the two muscles in the three positions. Although most reports neglect the action of the flexor and extensor carpi ulnaris muscles in flexing the elbow, these muscles cross this joint and can consequently, act on it as well as on the carpus.