Renawal systems in the visual cells and pigment epithelium of the vertebrate retina are being analyzed by administering radioactive precursors to living cells, in vitro or in vivo, followed by analysis of the distribution of radioactivity at different intervals after administration using mainly the technique of autoradiography. Most of the studies are being carried out in the frog. Current emphasis is on studies of the renewal of lipid and carbohydrate, with particular attention being given to renewal of the outer segments of the visual cells.