Electrophoretic modifications have been found in extracts from human and bovine lenses for three enzymes: glucose-6-phosphate dehydrogenase, triosephosphate isomerase and nucleoside phosphorylase. Increased anodic mobility is observed in all cases. It is more pronounced than in red cell lysates, also more evident in lenses from adult than from young animals. These results give evidence of posttranslational "aging" of enzyme molecules in lenses.