Standard grafts and nerve-intact grafts of the extensor digitorum longus muscle were compared in the rat. In standard grafts the muscle was completely removed from its bed and replaced; nerve-intact grafts were treated in an identical manner except that the muscle nerve was not severed. Nerve-intact grafts underwent the same sequence of skeletal muscle fibre degeneration and regeneration as standard grafts. In nerve-intact grafts the intramuscular portions of the nerve fibres initially degenerated, but within a week new nerve fibres had regenerated back to the original zone of motor end-plates. By 60 days the weight of nerve-intact grafts approached those of control muscles. Contractile tension in nerve-intact grafts was greater than that of standard grafts. In standard and nerve-intact grafts choline acetyltransferase activity rapidly decreased to low values and then increased along curves roughly paralleling the muscle weights. In nerve-intact grafts, neuromuscular transmission was established early in the second week whereas a considerably later return was seen in standard grafts. Either the early onset or the topographical pattern of reinnervation are potentially major factors in determining the success of free muscle grafts.

Critical period in muscle spindle regeneration in grafts of developing rat muscles