Abstract.Mitochondrial ultrastructure in the cells of coleoptiles of 4 d seedlings was investigated under conditions of a 1.5, 3, and 36 h anoxia and with subsequent transfer of the seedlings, after a 1.5 h anoxia, from the anaerobic into an aerobic medium. Even with short‐term anoxia (1.5 h) destructive changes take place in the ultrastructure of mitochondria, which are reversible not only following the transfer of these seedlings from the anaerobic into aerobic conditions, but also with their continued maintenance under strict anoxia. Irreversible changes in the ultrastructure of mitochondria were seen only with a more prologed (36 h and longer) anoxia. The observed phenomena are discussed from the viewpoint of energy provision of the seedling cells in anoxia and post‐ano