The work of various investigators indicates that the lens consumes oxygen and that the amount of oxygen consumption differs in different portions of the lens. Ely (1949) has shown that the capsules and nuclei of both bovine and rabbit lenses have a negligible respiration, that the cortex and epithelium are the only parts that respire, with the epithelium probably playing the dominant role in the oxygen uptake. Kinsey and Frohman (1951) from their findings on the distribution of flavoprotein, cytochrome-cytochrome oxidase, and lactatepyruvate ratios in different portions of the lens have concluded that the epithelium appears to have a strictly aerobic type of metabolism, while the cortex and nucleus seem to have an anaerobic metabolism. In order to investigate further the role played by the epithelium in the respiration of the lens, the effect of various oxygen tensions on cultures of growing human lens epithelium was studied. Cultures of lens