Published information concerning the influence of temperature in the physiological range (0-40 degrees) on various aspects of the visual process in invertebrates and vertebrates (poikilotherms and homeotherms) is reviewed. Bleaching and regeneration of scotopic and photopic pigments is influenced by temperature; so is the porphyropsin-rhodopsin ratio in fresh-water fishes. Effect on electrophysiological responses such as early receptor potential (ERP), electroretinogram (ERG) and its flicker fusion frequencies (FFF), S-potentials, glial membrane optic nerve and brain responses is presented. Histophysiological responses such as photomechanical or retinomotor responses are influenced by temperature. It also affects behavioural responses such as innate light reflexes, colour change, sensitivity, threshold acuity, FFF, spectral sensitivity and conditioned responses. General aspects such as oxygen consumption of the retina, acid formation and survival times are discussed with reference to their modification by temperature. Theoretical aspects such as the interaction between light and thermal energy in the absorption of a photon by a molecule, and available equations for comparing the effect of temperature on biological processes are also discussed. An attempt is made to draw a coherent picture and to discuss the significance of the thermal influence on vision to the animal. New avenues of research are also indicated. One hundred and eighty-eight (188) references are cited.