Patients with pigmented vitreous membranes were subjected to partial vitrectomy, and the membranes were studied by light and electron microscopy. Two yellow ochre membranes from eyes removed at autopsy were also examined. The membranes were composed of degenerating red cells and a delicate matrix of collagen. Phagocytic cells of uncertain origin and migrating retinal pigment epithelial cells were present in some of the membranes. Vascular channels were observed in only two cases, in which the membranes had clinical features different from those in the remaining cases. The development of new techniques of vitrectomy and the relatively normal clinical appearance of the posterior pole of the retina in these cases both suggest the potential clinical value of vitreous membrane excision. Additional histopathologic studies of vitrectomy specimens will enhance our understanding of the indications for this procedure.