Random matching of regenerating axons with Schwann tubes in the distal nerve stump is thought to contribute to the often poor results of peripheral nerve repair. Motor axons would be led to sensory end organs and sensory axons to motor end plates; both would remain functionless. However, the ability of regenerating axons to differentiate between sensory and motor environments has not been adequately examined. The experiments reported here evaluated the behavior of regenerating motor axons when given equal access to distal sensory and motor nerve stumps across an unstructured gap. "Y"-shape silicon chambers were implanted within the rat femoral nerve with the proximal motor branch as axon source in the base of the Y. The distal sensory and motor branches served as targets in the branches of the Y, and were placed 2 or 5 mm from the axon source. After 2 months for axon regeneration, horseradish peroxidase was used to label the motoneurons projecting axons into either the motor or the sensory stump. Equal numbers of motoneurons were labeled from the sensory and motor stumps at 2 mm, but significantly more motoneurons were labeled from the motor stump at 5 mm. (P = 0.016). This finding is consistent with selective reinnervation of the motor stump. Augmentation of this phenomenon to produce specific reunion of individual motor axons could dramatically improve the results of nerve suture.