Both free and adsorbed lactoperoxidase (LPO) were shown to produce the bacterial inhibitor, hypothiocyanite ion (OSCN––) in approximately equal capacity. In human salivary sediment OSCN–– ions are rapidly decomposed, even at pH 7.0 were OSCN–– ions otherwise are stable, indicating the presence of destructive agencies in sediment. Hypothiocyanite ions formed within the sediment inhibited acid formation clearly more than OSCN–– ions applied from outside. Iodide ions present in saliva inhibited competitively OSCN–– i