The extraction of acetone-dried bacteria by means of tris-glycine buffer has been found to yield the greatest number of antigens. Thus, up to 16 antigenic components with different electrophoretic mobility have been revealed in Y. enterocolitica. They include 4 thermostable proteins and 2 glycoproteins. Such antigens may be common and specific for each serovar. The presence of 1-3 surface antigens in common with the causative agent of plague has been revealed. Of these, the most active antigen has proteinaceous nature, and its mobility corresponds to that of rho-globulin. It is not identical with the surface Y. pestis antigen located in the albumin zone.