The percentage of high molecular weight protein aggregates obtained by Sepharose 6B column chromatography was increased significantly at pH 9.0 as compared to that of at pH 4.0 and 7.0, especially by exposure to light. The authors suggest that aggregation of lens protein is induced by light-exposure in the presence of riboflavin at higher pH's and that riboflavin acts as a photosensitizer to form high molecular weight protein aggregates in the lens.