Objective To investigate the longitudinal changes of macrophages and major histocompatibility complex (MHC) class Ⅱ-positive cells in the iris and ciliary body of Lewis rats after lipopolysaccharide (LPS) injection.Methods Immunohistochemistry was performed using monoclonal antibodies to monocytes and macrophages (ED1) and MHC class Ⅱ-positive cells (OX6) on wholemounts of the iris and ciliary body in endotoxin-induced uveitis (EIU).Results A network of macrophages (ED1+ cell) and MHC class Ⅱ-positive cells, was present in the iris and ciliary body of normal Lewis rats. Most cells in the iris and ciliary body displayed dendritiform appearance. A severe involvement of the iris and ciliary body, as evidenced by a rapid influx of monocytes and macrophages and remarkable increase of MHC class Ⅱ-positive cells, was observed after LPS injection. Conclusions A network of macrophages and MHC class Ⅱ-positive cells in the iris and ciliary body may play an important role in immune surveillance. LPS injection induces a severe inflammation in the anterior segment of the eye, which may serve as a model for acute anterior uveitis in human.