SUMMARY : Oakley & Warrack (1950) established the presence of two serologically distinct proteolytic enzymes in Clostridium histolyticum filtrates, a p-toxin digesting native collagen and a cysteine-activated y-toxin attacking azocoll and other protein substrates. In the present paper we give evidence of another proteolytic enzyme, not acti- vated by cysteine and serologically different from those previously described. This we designate as &-toxin. We also indicate the possibility of the presence of a fourth enzyme more stable than the others and active against various synthetic substrates in conjunction with cysteine. This enzyme could not be inhibited by antisera. Furthermore peptidases have been detected and will be described in detail elsewhere. Some of the differences between these enzyme systems are discussed. Several papers have been published on the various toxins and enzymes present in culture filtrates of Clostridium histolyticum, the most important studies being those of Oakley & Warrack (1950) who were able by serological methods to define three factors : the a-toxin, which is the main lethal toxin, the /$toxin, a collagenase, and the y-toxin, which is a cysteine-activated proteinase. Bowen (1052) and Howard (1953) published evidence for a distinct haemolysin com- ponent antigenically related to C. welchii &toxin and to tetanolysin. There