The cell-wall-associated proteolytic systems of several Streptococcus cremoris strains were analyzed by crossed immunoelectrophoresis. At least four immunologically different components of the proteolytic system's were found. One of these proteins was produced by all strains tested. The proteolytic activity of this enzyme was demonstrated with a zymogram staining technique which is based on the degradation of Coomassie-brilliant-blue-stainable casein. The crossed-immunoelectrophoresis patterns of the proteolytic systems of different S. cremoris strains indicated that each strain produces a characteristic combination of proteins. On the basis of these combinations, the different S. cremoris strains were classified into four groups.