An immunohistological study was performed in specimens of epiretinal membranes obtained during surgery in patients with proliferative diabetic retinopathy or retinal detachment with proliferative vitreoretinopathy. Using immunostaining procedures, these membranes were found to contain great amounts of immunoglobulins and complement, as well as a strong expression of class II antigens. These results confirm the involvement of auto-immune phenomena in intra-ocular proliferative diseases and the close relationship between the immune system and peptide growth factors.