One reason for failure of nerve recovery after suture or nerve grafting is the inappropriate matching of motor and sensory fibers. Methods used in attempting to solve this problem have either been unprecise, too time consuming, or unpleasant to the patient. Both experimentally and on cadaver samples, the level of choline acetylase activity is eight times higher in motor nerve fascicles than in sensory fascicles. In experimentally cut nerves, the ChAC activity remained high even after a period of 45 days. Thus it was possible to identify both ends of the motor and sensory fascicles in fresh injuries, and the proximal parts in old injuries. We have since used this method of intraoperative nerve identification in three patients. It has proved to be a rapid (70-80 minutes), viable technique for the immediate differentiation between proximal parts of motor and sensory nerve fascicles in cases of old nerve injuries. In contrast to our animal studies we found that the ChAC activity in the distal segment was still different for the various fascicles five months after transection. Presumably the present need for distal exploration to identify the "target organ" can be avoided.