The renewal of photoreceptor cell outer segments was studied using radioactive autography in rats, mice, and frogs. In all three species, labeled methionine was initially concentrated in the inner segment and then displaced to the base of the outer segment, where it accumulated as a distinct reaction band. This band gradually moved along the outer segment and eventually disappeared at the apex, indicating continuous renewal through the apposition of new membranous discs at the base and removal at the apex. The renewal rate was accelerated in frogs at higher temperatures and in both frogs and rats under high illumination. In rats, the reaction band formed in the inner segment and moved along the outer segment over several days. In 8-week-old rats, two injections of methionine-3H resulted in two reaction bands, indicating lamellar apposition. In mice, similar results were observed. In frogs, the reaction band formed at the base of the outer segment and moved sclerally, with the rate of movement influenced by temperature and illumination. At higher temperatures, the band moved more rapidly, and under high illumination, the movement was also increased. The outer segment is composed of a stack of membranous discs, and its renewal involves the continuous addition of new discs at the base and removal at the apex. The renewal process is supported by the synthesis of proteins in the myoid region of the inner segment, which are then transported to the outer segment. The removal of material occurs at the apical end, where it is phagocytized and absorbed by the retinal pigment epithelium. The findings suggest that the outer segment renewal is a dynamic process involving the formation of new discs and the removal of old ones, with temperature and illumination affecting the rate of renewal.The renewal of photoreceptor cell outer segments was studied using radioactive autography in rats, mice, and frogs. In all three species, labeled methionine was initially concentrated in the inner segment and then displaced to the base of the outer segment, where it accumulated as a distinct reaction band. This band gradually moved along the outer segment and eventually disappeared at the apex, indicating continuous renewal through the apposition of new membranous discs at the base and removal at the apex. The renewal rate was accelerated in frogs at higher temperatures and in both frogs and rats under high illumination. In rats, the reaction band formed in the inner segment and moved along the outer segment over several days. In 8-week-old rats, two injections of methionine-3H resulted in two reaction bands, indicating lamellar apposition. In mice, similar results were observed. In frogs, the reaction band formed at the base of the outer segment and moved sclerally, with the rate of movement influenced by temperature and illumination. At higher temperatures, the band moved more rapidly, and under high illumination, the movement was also increased. The outer segment is composed of a stack of membranous discs, and its renewal involves the continuous addition of new discs at the base and removal at the apex. The renewal process is supported by the synthesis of proteins in the myoid region of the inner segment, which are then transported to the outer segment. The removal of material occurs at the apical end, where it is phagocytized and absorbed by the retinal pigment epithelium. The findings suggest that the outer segment renewal is a dynamic process involving the formation of new discs and the removal of old ones, with temperature and illumination affecting the rate of renewal.