We examined the expression of osteopontin (OPN) in the sciatic nerves of rats with experimental autoimmune neuritis (EAN), using immunohistochemistry and immunoblotting, to study its involvement in the pathogenesis of autoimmune peripheral nervous system diseases. Constitutive OPN expression was detected in some Schwann cells; expression was increased after immunization with adjuvant alone. At day 14 after induction of EAN, many Schwann cells had a granular pattern of immunoreactivity, whereas very few inflammatory cells were OPN-positive. Even after recovery from hindlimb paralysis, at 24 days post-immunization, OPN expression remained elevated in the Schwann cells. The results suggest that OPN expression in Schwann cells is easily induced by immunostimulation, and further enhanced by the inflammatory reaction in EAN. Continued elevation of OPN after recovery may represent a functional recovery after a transient inflammatory insult.