Previous studies have suggested that changes occur in low molecular weight proteins during the progression of human senile cataract. In this report we have employed the reverse phase mode of high performance liquid chromatography (HPLC) and characterized the patterns of changes in the fractions of low molecular weight substances. Two different types of cataractous lenses, brown and yellow types, were used. Classification of cataract stages in each type was determined by measuring the Na+/K+ ratio in each lens. The profile of low molecular weight substances loosely bound to the reverse phase column changed significantly during cataract progression. In the brown type cataractous lenses, however, the low molecular weight substances changed after the middle stage of cataract progression, while in the yellow type cataractous lenses, the changes started during the early stages of cataract development. These experiments demonstrated that the reverse phase mode of HPLC is a sensitive and specific method for characterization of the quantitative differences in low molecular weight compounds during the progression of human senile cataract.