Extensive work with lens epithelial samples from human donor lenses has been undertaken to determine what alterations occur during aging in these cells. The samples have been studied with two-dimensional gel electrophoresis to investigate possible polypeptide differences in the various regions of the epithelium. Surprisingly few differences could be detected in the three major zones of the adult human epithelium with respect to the major polypeptides and there were only minor differences in the epithelium with age, These results suggest that the epithelium of the lens might be a useful source of material with which to investigate cataractous changes in specimens obtained after surgical removal. As an adjunct to the studies on the human lens epithelium, studies were also conducted with epithelium from monkey lenses. The purpose of these experiments was to determine what changes might occur during conditions commonly used to store human donor material. Lens epithelium stored about 50 hours appeared by two-dimensional gel electrophoresis to be identical to freshly obtained specimens. Efforts to develop in vitro systems to check the efficacy of anti- cataract agents have concentrated on the study of a lens epithelial cell line from a transgenic mouse. The cell line has been used to investigate the formation of the partially differentiated structures known as lentoid bodies. In addition, experiments have been started to study alterations in metabolism that occur during oxidative stress. Data from these studies will expand our understanding of age-related cataract development.