Surface membranes of intraocular lenses implanted in three rabbit, were studied immunohistochemically with anti-rabbit fibronectin serum and anti-rabbit whole serum antiserum. The specimens were embedded in an epoxy resin and cut at 1 micron. Before the immunostaining procedure, the sections were placed in a solution of saturated NaOH in absolute ethanol to remove the epoxy resin. Immunostaining procedure was performed by routine avidin-biotin-peroxidase technique. The surface membranes showed positive reactions against both anti-sera. These results indicated that the surface membrane of implanted intraocular lenses was composed of fibronectin with some other serum proteins.