During intraocular silicon oil tamponade, recurrent vitreoretinal membranes can become clinically relevant and may need surgical excision. We investigated 40 PVR and 10 diabetic membranes which had formed during intraocular tamponade with highly purified silicone oil (5000 cs). The membranes were investigated by light and electron microscopy with respect to silicone oil-specific alterations. The participating cells were differentiated immunohistochemically. Mechanisms of intercellular growth regulation were analyzed by the use of antibodies against cell adhesion molecules and growth factor receptors (PDGFr-B). Most of the membranes showed typical signs of the underlying disease process. However, seven PVR and four diabetic membranes had specific interstitial and intracellular vacuoles which were considered to be silicone oil droplets. The phagocytosing cells were macrophages, partially embedded within vitreous residues. T-lymphocytes can be drawn to the area of macrophage activity by the expression of ICAM-1 and LFA-1. The residual parts of the membranes are typical vitreoretinal membranes. The receptors for PDGF, fibronectin and laminin were negative, but the receptors for collagen and vitronectin were positive within these membranes. The silicone oil-specific macrophage reaction might be supported by emulsified silicone oil droplets, which might get phagocytosed at a certain size. The secondary inflammatory reactions can further enhance silicone oil emulsification and start a vicious circle. Nevertheless, the underlying disease process seems to be much more important in stimulating recurrent membrane formation than silicone oil-specific cell reactions.