Whole cells of bakers' yeast (Saccharomyces cerevisiae) exhibited very low catalase activity (16 U g(-1)). Various treatments altered membrane permeability and increased cellular catalase activity. Treatment with cetyltrimethylammonium bromide (CTAB) yielded maximum catalase activity (51000 U g(-1)) followed by digitonin (27072 U g(-1)). After permeabilization of the membrane, the catalase slowly leaks out of the cells. The half-life of intracellular catalase in CTAB-permeabilized cells was 3.4 days at 4 degrees C and 1.2 days at 26 degrees C. Catalase in permeabilized cells was more stable against self-inactivation during catalysis than the enzyme in cell-free extract and purified catalase. Catalase of CTAB-permeabilized cells was effective in removing the residual H2O2 from H2O2-treated fresh milk/heat pasteurized milk.