Editor,—A new protease enzyme in the human lens, dipeptidase, has been purified to homogeneity and characterised recently by Sulochana et al.1This enzyme is specific for dipeptides in its protease function while two other lens proteases, leucine amino peptidase2 and amino peptidase III,3 can act on di-, tri-, and oligopeptides. It is reported that the activity of amino peptidase III did not change with age but the specific activity decreased in human cataract lenses.4 Two viewpoints on the role of such proteases have been discussed by earlier workers—namely, a …