We have previously shown that biologically uncommon D-beta -aspartic acids (Asp) were localized with very high contents at Asp-151 and Asp-58 of alpha A-crystallin from aged human lenses. The amounts increased with age, and we have proposed the mechanism of this reaction. In the present study, in order to elucidate the possible relationship between the formation of D-beta -aspartic acids in alpha A-crystallin and cataract formation, we measured the D/L ratio of beta -Asp-151 of alpha A-crystallin from both cataractous and age-matched normal human lenses, alpha A-crystallin from total proteins of cataractous and age-matched normal lenses was prepared, followed by tryptic digestion and quantification of D/L ratios for tryptic fragments containing the alpha- and beta -aspartate forms of Asp-151 residues. The results demonstrate that the D/L ratio of beta -Asp-151 of alpha A-crystallin from normal lenses is not statistically significant from that of alpha A-crystallin from cataractous lenses, suggesting that formation of this biologically uncommon amino acid may not play a role in human cataractogenesis.