Cell growth in proliferative vitreoretinopathy (PVR) is activated by naturally occurring mitogenic substances; thus, growth factors seem to play an important role in PVR. Cell activation by growth factors requires the presence of specific cell-bound receptors by which the mitogenic signal is transmitted. Using the indirect immunoperoxidase method, we investigated frozen sections of 15 epiretinal membranes in PVR for the presence of epidermal growth factor receptor (EGFR), which is commonly utilized by epidermal growth factor (EGF) and transforming growth factor-alpha (TGF-alpha). This receptor could be localized only in one epiretinal membrane. The receptor-bearing cells stained positively for vimentin, cytokeratin, and macrophage marker Ki-M7, indicating that they most probably correspond to transformed macrophages. They stained negatively for desmin and glial fibrillary acidic protein. The cells were embedded in a fibronectin-positive intercellular matrix and were in an actively proliferating state as demonstrated by positive staining for the nuclear proliferation marker Ki-67. We propose that EGFR might be expressed only in certain as yet undefined stages of PVR.