The authors studied the transmission electron microscopy characteristics of retroretinal membranes surgically removed from 20 human eyes with proliferative vitreoretinopathy. Retinal pigment epithelium was the predominant cell type. Other cells included fibrocytes, macrophages, fibrous astrocytes, and myofibrocytes. Fibrin and collagen were also present. The cellular and extracellular constituents of these retroretinal membranes are similar to findings in previous reports of retroretinal membranes removed during vitreous surgery, as well as experimentally induced retroretinal membranes in animals. RETINA 8:275-281, 1988