Objective To investigate the changes at the motor end-plate (i. e. neuromuscular junction) following the free neurovascular muscle transfer. Methods Light and electron microscopy were used to study serially during 30 weeks the changes at the neuromuscular junction after free muscle transfer of the gracilis muscle in the adult Wistar rat. Results Under light microscopy, after staining with acetylthocholine the neuromuscular junction showed changes of degeneration with withdrawal of the innervating axon terminal followed by regeneration and reconstitution of the neuromuscular junction. With the electron microscope, mitochondrial sweelling and clumping of the synaptic vesicles were followed by withdrawal of the axon terminal from the muscle membrane on denervation. The infolding of the muscle membrane at the neuromuscular junction became less prominent. With reinnervation the ulatrastructure of the junction was only partially reestablishied with poorly reconstituted primary and secondary folds of the muscle membrane. The newly formed neuromuscular junction still lacked the structural detail seen in the control neuromuscular junction, even after 30 weeks. Conclusion The persistent weakness following free neurovascular muscle transfer may be attributed to the failure of full recovery of the intricate ultrastructure of the neuromuscular junction.