In the present review dealing with the antibacterial lactoperoxidase (LP) system, it is shown that the two reactants thiocyanate (SCN-) and hydrogen peroxide (H2O2) as well as the catalytic enzyme lactoperoxidase (LP) are widely distributed in nature and that evidence for the activity of the LP system in animals, including man, is accumulating. The in vitro effects on bacterial and animal cells are discussed and the unique action of the LP system on the bacterial cytoplasmic membrane is pointed out. Some practical applications are also presented, with particular emphses on the possibility of utilizing the LP system to preserve the quality of raw, cooled as well as uncooled milk. It is concluded that the addition of minute quantities of SCN- and H2O2 (ca. 12 and 8 ppm, respectively) to secure an optimum activity of the LP system should be harmless to the consumer of milk and milk products treated in this way.