Single discrete muscle fibers were found in regenerating motor nerves in adult crayfish. The regenerating nerves were from native or transplanted ganglia in the third abdominal segments and consisted of several motor axons. The proximal end of these motor axons showed numerous sprouts. Muscle fibers in these regenerating nerves appeared newly developed and were innervated by excitatory nerve terminals. A likely source of these novel muscle fibers may be blood cells in the nerve or satellite cells from neighboring muscle. Contacts made by axon sprouts with other axon sprouts, glia, and muscle fiber, in the form of a dense bar with clustered clear vesicles, characterized the regenerating nerve. These contacts may provide a possible signaling pathway for axon regeneration and myogenesis.