The antibacterial effect of the lactoperoxidase/thiocyanate/hydrogen peroxide system (lactoperoxidase system) was tested against strains of Campylobacter jejuni and Campylobacter coli isolated from poultry. The effect was studied at different pH-values and temperatures in UHT-milk (control); UHT-milk containing lactoperoxidase, sodiumthiocyanate and hydrogen peroxide (lactoperoxidase system); UHT-milk containing lactoperoxidase, sodiumthiocyanate, hydrogen peroxide and sodiumpyrosulfite (inactivated lactoperoxidase system). The lactoperoxidase system had a strong bactericidal effect against C. jejuni and C. coli. The bactericidal effect was more rapid at 37°C compared to 20°C. The effect of lactoperoxidase system decreased with decreasing pH-values. The fastest reduction in viable numbers was obtained at pH 6.6 and 37°C.