α-Crystallin, isolated from bovine lenses by vertical-column zone electrophoresis, has been separated into two fractions by chromatography on deae -cellulose. The two fractions gave single precipitation lines in immunodiffusion and immunoelectrophoresis experiments. They exhibited a marked difference in their free-electrophoretic mobility at pH 8·0 and a small difference in their sedimentation constants, but their amino acid composition, amide group content, intrinsic viscosity, optical rotatory dispersion and molecular weight, as determined by light scattering, were the same. Furthermore, double-diffusion tests revealed an immunological identity between the fractions. These observations suggest either that the two fractions possess slightly different secondary or tertiary structures or that one of the fractions contains a larger amount of an electrically charged compound bound to the protein molecule. The relative proportions of the two fractions in the lens were found to vary considerably with the age of the animal, indicating a transformation of α-crystallin in the lens during the life span of the animal or a slightly different mechanism for the synthesis of α-crystallin in young and old lenses.