Nineteen cases of epiretinal membrane (ERM) in proliferative diabetic retinopathy were studied using immunohistochemical methods. Antibodies against type I-IV collagen, fibronectin (FN), glial fibrillary acidic protein (GFAP), vimentin and the monoclonal antibody (MAB) against human Müller cells were used to examine the membranes. Type II collagen was found on one side of the ERMs in 95% of the cases. The other types of collagen, FN and vimentin were also identified in most cases. Müller cells (GFAP- and MAB-positive) were found in 2/19 cases (11%), and astrocytes (GFAP-positive but MAB-negative) were found in 10/19 cases (53%). These results suggest that type II collagen (vitreal collagen) may act as a scaffolding in the formation of ERMs and that glial elements of the ERMs consist mainly of astrocytes.