Treatment of normal lens homogenates with trypsin results in the production of polypeptides of approximately 4,000 and 8,000 daltons. Peptide maps of these components are very similar to polypeptides of comparable molecular weight found only in cataracts with brunescent and opaque nuclei. Together, these results demonstrate that putative proteolysis products producedin vivoduring human cataractogenesis can be mimicedin vitroby the addition of exogeneous proteases to the normal lens homogenate.