The lens crystallins were analyzed in normal dogs and Miniature Schnauzer dogs with congenital cataract formation. There was an increase in the relative proportions of α and β L -crystallin and a decrease in βH and γ -crystallin with increasing age in the noncataractous lens. These trends were advanced in the age-matched cataractous lenses. “Advanced aging” trends were also noted in various polypeptide components of β-crystallin. Specifically, the appearance of a 29K band as well as a reversal of the 26K to 27.6K ratio occurred at an earlier age in the cataractous lens than in the clear lens. Three subunits of approximately 19K, 20K, and 21.5K were present on SDS-PAGE for α-crystallin from the cataractous lens as opposed to only two of 19K and 21.5K from the clear lens. However, if the protein was not heated following resolubilization in buffer containing 2% SDS and 5% 2-mercaptoethanol, only two subunits of 20K and 21.5K were evident in both clear and cataractous lenses. The electrophoretic behavior observed for both α and γ-crystallins did not appear to be age related.