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The role of reduced glutathione (GSH) in lens membrane function was studied by depleting GSH with 1-chloro-2,4-dinitrobenzene (CDNB), a reaction catalyzed by GSH-S-transferase. Depletion of GSH in the lens epithelium by 70–90% led to a decrease in uptake and increase in efflux of ⁸⁶Rb. ATP levels and Na⁺/K⁺-ATPase activity were normal while there was a slight decrease in lactate production. The results provide the first direct evidence that depletion of endogenous GSH per se does not lead to inactivation of Na⁺/K⁺-ATPase. However, lenses deficient in GSH when challenged with a normally tolerated level of H₂O₂ showed significant inactivation of membrane ATPase without a further increase in membrane permeability. Pretreatment with CDNB resulted in a 3-fold stimulation of the hexose monophosphate shunt activity which is attributed to the unexpected finding of a significant increase in the level of oxidized glutathione in the lens. It is concluded that deficiency of GSH causes a marked increase in membrane permeability and such lenses are susceptible to oxidative damage resulting in inactivation of the Na⁺/K⁺ pump, thus leading to ionic changes and cataract development.