Since the early 1960s, measurements of the absorbance spectra of both photosensitive and inert pigments within intact isolated visual receptor cells have been achieved in a great number of species, including representatives of all the vertebrate groups as well as some invertebrates, principally the insects. The technique has meant a rapid advance in our understanding of the basis of colour vision throughout the animal kingdom as well as increasing our knowledge of the behaviour of visual pigments in situ. A review of these advances, especially within the fish, birds and primates is presented with emphasis on the limitations of the technique, and the intriguing questions that microspectrophotometric analysis of the pigments of visual receptor cells has raised.