Ammonia, as metabolite of microbial activity, was confirmed to be a suitable rapid monitoring index of the total hygienic quality of large mass raw milk. A 0.82 correlation was found between the total bacterial count and NH3, which we feel to be particularly influenced by the psycrophilic microflora. The standard and action-level values useful for rapid selection of milk are suggested. The value of the NH3 content of raw milk does not change after the pasteurization treatment, and can be used as a quality index of the pasteurized milk of unknow hygienic history. The behaviour of NH3 of pasteurized milk was investigated under cold storage conditions.