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Hypoxic pretreatment (H-PT; incubated in 5% O2 atmospherefor 24 h) greatly improved subsequent tolerance of anoxia in theprimary roots of Avena sativa. Survival of H-PT roots inanoxia increased by 6.4-fold compared to that of non-pretreated (N-PT) roots ofthe seedlings. ATP concentration in the H-PT roots was 4.8-fold greater thanthat in the N-PT roots at 12 h after onset of anoxia. Duringpretreatment periods, alcohol dehydrogenase (EC 1.1.1.1) and pyruvatedecarboxylase (EC 4.1.1.1) activities in the roots became 7.5- and 4.3-foldgreater than those in the N-PT roots, respectively. After the onset of anoxicstress, their activities in the H-PT roots remained greater than those in theN-PT roots, and the average production rate of ethanol was much greater in theH-PT roots than N-PT roots. These results suggest that the H-PT may increaseanoxia tolerance due to maintenance of anaerobic glycolysis with induction ofethanolic fermentation to generate ATP.