Our purpose is to report our experiments in the preparation of serologically pure fractional antigens of the crystalline lens, and our observations on the chemical and immunologic properties of these fractions. This study was undertaken as the necessary forerunner of a proposed study of the possible rôle lens protein may play in lenticular disease. Before reporting our observations, the problem would be made somewhat clearer by a brief historical review. In 1894, Morner1isolated from beef lens two crystalline fractions, which he called "lens alpha" and "lens beta," and an insoluble substance which he termed "albuminoid." In 1910 and again in 1922, Jess2reported his studies on the quantitative relationship of the alpha and beta crystallin at different ages, and in the normal and pathologic lens, noting the fact that in old age and in cataractous lenses the amount of the alpha fraction was decreased. In 1903, Uhlenhuth