The use of human Schwann cells (SCs) in transplantation to promote regeneration in central and peripheral neural tissues must be preceded by efforts to define the factors that regulate their functional expression. Adult-derived human SCs can be isolated and purified in culture, but the culture conditions that allow their full differentiation have not yet been defined. We tested the functional capacity of these cells to enhance axonal regeneration and myelinate regenerating axons in vivo by transplanting them into the damaged PNS of an immune-deficient rat. SCs were purified from human peripheral nerve obtained from organ donors. Semi-permeable guidance channels were filled with a 30% Matrigel containing solution with or without human SCs suspended at a density of 80 x 10(6) cells/ml. Channels were implanted within an 8 mm gap of the transfected sciatic nerve of nude female rats for a period of 4 weeks. Survival of the transplanted human SCs was established by dissociating nerve explants taken from the regenerated cable (after first placing them in culture for 5 d) and staining individual cells for a primate-specific NGF receptor (PNGFr) and S 100. Only one-half of the S 100-positive cells stained for the PNGFr, which indicated that the regenerated cable contained an approximately equal number of human and rat (host) SCs. The presence of some human myelin segments was confirmed by immune staining with an HNK- 1 antibody that specifically labels human but not rat myelin. The majority of the myelin segments in the regenerated cable, however, were produced by the rat SCs. The number of myelinated axons and the cross- sectional area of the cable were significantly greater in channels seeded with human SCs when compared to channels containing the diluted Matrigel solution alone. We conclude that purified cultured human SCs can survive and substantially enhance axonal regeneration when transplanted into the injured PNS of an immune-deficient rat. Some of the transplanted human SCs are capable of myelinating regenerating rat axons but are less successful than the host SCs.