We did Cybex testing of thirteen patients who had had a rupture of the distal tendon of the biceps brachii. The tests were performed fifteen months to six years after injury. The ten patients who had had a surgical repair through the two-incision technique showed a return to normal levels of strength and endurance with regard to both flexion of the elbow and supination of the forearm. The three patients who had had conservative treatment showed a remaining deficit in those parameters which was clinically evident in several activities, such as use of a screwdriver or baseball bat.