The effect of the inhibitors of aerobic metabolism on the transport of rubidium and ATP content in rat lens has been studied under organ culture system. The inhibitors used were malonate, monofluoroacetate, cyanide, antimycin A, 2-heptyl-4-hydroxyquinoline-N-oxide (HQNO), 2,4-dinitrophenol (DNP) and dicumarol. All these compounds inhibited the transport of rubidium, reflecting a decrease in the ability of the lens to transport potassium. The levels of ATP also decreased. The results were similar to those obtained under anaerobic conditions where the lenses were incubated in a nitrogen atmosphere without the inhibitors. The degree of inhibition observed by the metabolic inhibitors as well as by anaerobiosis indicate that the rat lens depends substantially on aerobic oxidation for its energy needs, unlike bovine and rabbit lenses studied before.