Purpose. Phagocytosis of rod outer segments (ROS) is an important function of retinal pigment epithelial (RPE) cells. Since the details of the process are not fully known, we studied effects of cytokines produced by RPE and photoreceptor cells on phagocytosis of ROS by rat RPE cells.Methods. RPE cells were isolated and cultivated from two strains of rats: Sprague-Dawley (SD) rats with normal phagocytosis and Royal College of Surgeons (RCS) rats, which have genetic deficiencies in ROS phagocytosis. A double immunofluorescence staining technique was used to study the effectsin vitroof several cytokines on phagocytosis of ROS.Results. We found that transforming growth factor beta-1 (TGF-β1) had dose-dependent effects on RPE cells of both strains of rat: at a concentration of 10 ng/ml, TGF-β1 significantly (p<0.01) reduced total ROS (to 74% of control in SD rats and to 51% of control in RCS rats), reduced bound ROS (to 56% of control in SD rats and to 48% in RCS rats), and increased the ratio of ingested ROS to total ROS (to 140% in SD rats but not significantly in RCS rats). Treatment of medium with anti-TGF-β1 antibody before incubation of RPE cells of SD rats with TGF-β1 decreased the magnitude of these effects. The cytokine acidic fibroblast growth factor (aFGF, 10 ng/ml) affected RPE cells of SD rats only, decreasing ROS ingested to 56% of control and the ratio of ingested ROS to total ROS to 64% of control. We also examined effects of basic fibroblast growth factor and insulin-like growth factor. None of the cytokines tested increased ingestion of ROS by RPE cells of RCS rats.Conclusions. Our results suggest that TGF-β1 and aFGF have roles in regulating ROS phagocytosis by normal and dystrophic RPE cells in the rat.