Reinnervation of composite-tissue allografts was examined in a rat hind-limb transplant model under Cyclosporin A (CyA) immunosuppression. Two groups of animals were studied. Group 1 consisted of 10 composite-tissue allografts using inbred Fisher rats (F344) as recipients and inbred Lewis rats (LEW) as donors. Recipient animals received 15 mg/kg/day CyA subcutaneously for three weeks and then twice weekly for three months. Group 2 consisted of 10 composite-tissue isografts undergoing no immunosuppression, and using F344 as both donors and recipients. Eight months after operation, electromyographic, histologic, and morphometric assessments of nerve regeneration were made. There were no significant electromyographic differences between these two experimental groups in amplitude and conduction velocity, but the levels were lower than in controls. The histologic patterns of nerve regeneration within the composite-tissue transfers were similar in the two groups. However, the fiber population in the regenerated nerves in the two groups was different from that in the normal sciatic nerve. This study confirmed the reinnervation of composite-tissue allografts under CyA immunosuppression. The quality of regeneration in allografts was similar to that in isografts, but the histologic and electromyographic properties of regenerated nerves were different from those of normal sciatic nerves.