Bifidobacterium bifidum (ATCC 15696) was grown in MRS broth containing cysteine.HCl at 37 degrees C, and the cells were harvested by centrifuging at 1300 x g for 15 min at 4 degrees C. Equal volumes of the cell slurry and a 2.5% solution of kappa-carrageenan were mixed and transferred by drops into a solution of .3 M KCl at 20 degrees C under an atmosphere of nitrogen. The gelled beads were separated, frozen, and lyophilized immediately. This preparation and a commercial powder preparation were added to Cheddar cheese curd at milling as two treatments. Treatments did not affect cheese composition. Soluble protein increased during ripening at 7 degrees C but without differences between treatments; SDS-PAGE patterns of proteolysis were also similar. Lactic acid content of cheeses increased during ripening, but differences between treatments were minor. Acetic acid and ethanol, common metabolites of bifidobacteria, were not detected during ripening. Bifidobacteria remained viable and increased in numbers in cheese during this 24-wk study but did not affect the flavor, flavor intensity, texture, or appearance of the cheese compared with that of the control.