Effect of oxygen and metabolic substrates (glucose, ethanol) on the catalase activity of anaerobically grown Schizosaccharomyces pombe cells was assessed and compared with that of Saccharomyces cerevisiae in order to determine the catalase activity regulation in S. pombe. In contrast to S. cerevisiae, the total catalase activity of permeabilized S. pombe anaerobically grown cells is higher than that found in aerobically grown cells, is stable and constant under all circumstances (i.e. it is not induced by oxygen and/or substrates), and only a negligible part (3-5%) of it is contributed by de novo protein synthesis during aeration with or without substrates. The patent catalase activity of intact cells rises 2-fold during 6-h aeration without substrate and 7-8-fold in the presence of glucose or ethanol. The increase is not inhibited by cycloheximide and is thus not due to de novo catalase synthesis, but may reflect enhanced transport of catalase to the cell surface or a permeabilization of the plasma membrane during the aeration.