A rapid and precise method of nerve fascicle identification based on measurement of choline acetyltransferase activity using radioisotope technique was used intraoperatively during upper extremity reconstruction. This technique can be used to evaluate the motor function of donor fascicles directly and quantitatively. This technique is useful to evaluate the motor functional status of donor fascicles during functioning free muscle transfer, to distinguish between preganglionic and postganglionic injuries in brachial plexus injury, and to differentiate between motor and sensory fascicles during nerve grafting procedures.