The high molar absorptivity (at 280 nm of γ-crystallin and the insoluble protein fraction derived from the ocular lens of the dogfish is due to the presence of a fluorescent compound. The fluorogen was isolated and purified and partially characterized by UV and fluorescence spectra. The structural proteins of the ocular lens in almost all species (except for the Avian species) consist of 3 soluble fractions known as α-, β- and γ-crystallins and an insoluble portion frequently referred to as the albuminoid fraction. In the γ-fraction derived from 4 species studied in this laboratory (rat, dogfish, bovine and human) anomalously high E<sup>1%</sup><sub>1cm</sub> values (at 280 nm) have been reported [1–3]. A similar situation has also been noted in the insoluble protein fraction derived from 2 species, namely the rat and dogfish lens. The purpose of this paper is to determine the basis for the high absorptivity in the 280 nm region observed with γ-crystallin and the insoluble protein fraction derived from the ocular lens of the dogfish (Mustella canis).