The specific aims of this study are: To study the unilization and storage of vitamin A in the eyes of the frog (Rana pipiens) by measuring the specific activity of rhodopsin and retinyl ester in frogs injected with 11-123H retinol and held under a light/dark cycle or in total darkness. Groups of frogs kept under cyclic light (12h darkness/12h light) will be injected with 3H retinol intraperitoneally. Their eyes will be removed at 2, 4, 12, 24, 48 hours, 7, 14, 32 and 60 days. The specific activity of the visual pigment in the retina will be estimated from the purified rod outer segments prepared according to the method of Papermaster and Dreyer (1974). The retinyl ester in the pigment epithelium will be extracted with acetone and then purified by alumina column. The estimation of quantities will be done by UV - vis spectroscopy and by Carr-Price Colorimetry. The change in the specific activity of rhodopsin, when compared to the change in the specific activity of retinyl ester, will enable us to understand whether vitamin A is first incorporated as visual pigments or as retinyl ester in the eye. The influence of light and darkness on this utilization process will also be relevant. By understanding exactly how the chromophore is employed to synthesize the visual pigment it will improve our current knowledge on the visual process of vertebrate photoreceptors. It is important to understand the physiological pathway of the normal visual system in order to explain and to resolve problems arising from abnormal and disease conditions.