During vitreoretinal surgery, 23 epiretinal membranes from eyes treated with silicone oil were removed. They were examined by immunohistochemical methods and compared with 15 membranes from eyes affected by proliferative vitreoretinopathy (PVR) and not treated with silicone oil and with 4 membranes from eyes with intermediate uveitis. PVR membranes from eyes treated with silicone oil showed a high level of macrophages and a strong expression of HLA-DR. Additionally, lymphocytes were found in PVR membranes, a finding that has not been described before. Similar changes were seen in proliferations removed from eyes affected by uveitis, but these membranes were found to have smaller amounts of extracellular substance. In contrast to this, most cells in the PVR membranes from eyes not treated with silicone oil react with vimentin, GFAP and cytokeratin. In none of these membranes were we able to find T-lymphocytes. It is not possible to say whether or not the different findings are attributable ot the silicone oil.