AbstractThe literature describing intermediates formed after photolysis of visual pigments is reviewed. Results obtained near physiological temperatures using time‐resolved optical density measurements in the UV/Vis region are emphasized. The general character of intermediates which appear in the course of protein function, and the role of methods with different time resolutions in their study, are discussed. Specific results for intermediates from bathorhodopsin to metarhodopsin II are treated in detail, with limited discussion of the earlier and later species. The discussion centers on the best‐understood pigment, bovine rhodopsin, but results for cone‐type and invertebrate pigments are also discussed. Comparison is made between the picture of the intermediates obtained using low‐temperature trapping methods and that obtained using kinetic measurements. The thermodynamic parameters of the intermediates are discussed, and their significance for the structure/function of heptahelical protein intermediates in general is con