Rhodopsin and related pigments will be studied using resonance Raman scattering techniques. This technique is a sensitive and powerful probe of in situ chromophore structure and state of protonation. Besides bovine rhodopsin, experimental work on bacteriorhodopsin, artificial pigments (made with retinal analogs) and model chromophores are envisioned. Theoretical studies will be undertaken in order to facilitate the interpretation of the data in detailed and reliable terms and reliable molecular models. There are three overall aims: (1) to define the structure of the chromophore site; (2) to determine the primary photochemical event; and (3) to determine the structure and reaction pathways of the dark intermediates that follow the formation of the primary photoproducts of rhodopsin and bacteriorhodopsin.