Immobilized lactase and glucose oxidase were used to produce H 2 O 2 to activate the lactoperoxidase system in milk. The enzymes were immobilized on nylon pellets. With a ratio of 35 g of catalyst/L of milk, a concentration of 0.75 mM was produced in 3 min. Raw milk treatment with the catalyst reduced coliforms by 79%; Staphylococcus aureus reduction was 68%, psychrotrophs 91%, and fungi 100%. Results were similar when milk was treated by addition of H 2 O 2 . Thiocyanate was not limiting because addition of NaSCN did not increase the effectiveness of the lactoperoxidase system.The stability of the catalyst was poor when successive treatments were applied to milk, having lost one half of the activity every eight determinations. Activation of the lactoperoxidase system by immobilized enzymes could be of interest if stability could be ensured.