A major component of human nuclear cataracts is water-insoluble, high molecular weight protein. A significant component of this protein is disulfide bonded gamma S-crystallin that can be reduced to monomers by dithiothreitol. Analysis of this reduced gamma S-crystallin showed that deamidation of glutamine and asparagine residues is a principal modification. Deamidation is one of the modifications of lens crystallins associated with aging and cataractogenesis. One proposed hypothesis of cataractogenesis is that it develops in response to altered surface charges that cause conformational changes, which, in turn, permit formation of disulfide bonds and crystallin insolubility. This report, showing deamidation among the disulfide bonded gamma S-crystallins from cataractous lenses, supports this hypothesis.