This study on rats was designed to evaluate the change of biceps muscle fibers by enzyme histochemical examination and the change of distribution of motoneurons innervating biceps muscle fibers by retrograde tracer examination after incomplete spinal cord injury. Incomplete spinal cord injury was produced by placing a 20 g weight on exposed dura at the C6 level. The number of the labeled motoneurons of C6 segment significantly decreased compared with that in the control, but there were no significant changes in the other segments at 4 weeks after the injury. Moreover, there was type grouping of biceps muscle fibers at 4 weeks after the injury. These findings indicated that the incomplete cervical spinal cord injury at C6 level in rats caused the partial denervation and then reinnervation of biceps muscle fibers by the collateral sprouting of the remaining motoneurons which belonged to the same motoneuron pool of the injured motoneurons.