Lens epithelial cells were isolated from samples of C57BL/6 and CD-I mice at different ages between 1 and 5 months, and assayed for the level of N-acetyl-β-glucosaminidase and their ability to replicatein-vitro. The lens epithelial cells from C57BL/6 mice had a reduced replicative potential compared to other normal strains. A statistically significant decrease in active enzyme levels was demonstrated to be associated with increased animal age of C57BL/6 mice.