Soluble proteins of individual human normal and nuclear cataractous lenses of 60-70-year-old subjects were collected for this investigation. The average wet weights of both the normal and nuclear cataractous lenses were found to be essentially identical, approximately 230 mg. When the lens proteins, either cortical or nuclear, were subjected to fractionation by Sephadex G-200 sf chromatography, six fractions (F-I to F-VI) were obtained and their respective molecular weights approximated. F-I, which contains alpha-crystallin and high molecular weight aggregates, was subsequently fractionated through a series of Bio-gel A chromatographic columns. The quantities of the proteins and the molecular weights of each fraction were obtained. All the proteins fractionated were subjected to SDS gel electrophoresis by which the molecular weights of the subunits were obtained. The distribution and molecular weights of proteins smaller than 0.2 X 10(6) showed certain changes, more noticeable in the nucleus than in the cortex, between the normal lens and nuclear cataractous lens. For the high-molecular-weight protein aggregates, the major fraction in the lens cortex was found to be in the 5-1.5 X 10(6) range, representing 10 and 12% of the total protein in the normal and cataractous lenses, respectively. The major fraction in the nucleus was found to be greater than 150 X 10(6), representing 11 and 19% for the normal and cataractous lenses respectively. The above data are presented for the first time to show the differences in distribution of the high-molecular-weight proteins in the cortical and nuclear regions, and their respective changes in cataractogenesis. Based upon these data, we are able to calculate the average molecular weights of (1) the soluble cortical and nuclear proteins and (2) the total soluble protein, in the normal and cataractous human lenses.