The Emory mouse develops a late-appearing hereditary cataract having many characteristics which suggest its usefulness as an animal model for human senile cataract. This paper presents some results of analyses designed to determine biochemical changes associated with initiation and development of the cataract. The measurements carried out include water-soluble and water-insoluble protein, glutathione, protein sulfhydryl, non-protein disulfide, sodium, potassium, calcium and free phosphate. The most useful and consistent index of cataract progression seems to be the conversion of soluble to insoluble protein, a change which in the normal aging mouse lens is accompanied by some conversion of total sulfhydryl to disulfide. Cataract development also produces a significant reduction in the glutathione concentration.