This work proves that the proteolytic action of leucocytes is not a simple cleavage by one ferment. There are present two proteases, one acting in an alkaline medium and the other in an acid medium. This confirms Opie's work. In the leucocytes there was found in addition an ereptic ferment which is capable of acting in an acid or alkaline medium. Since this action is lost by heating to 70°C., and by drying and keeping the leucocytes, it probably represents a ferment which acts on the digestion products of the two proteases. Analogy with other ferments in the body confirms this opinion.