Swine were vaccinated with adsorbate bacterin made from Erysipelothrix rhusiopathiae of serotype 2 and were subsequently allotted to 4 exposure groups, each of which was exposed to 1 of the strains of E rhusiopathiae of serotypes 1, 2, 9, or 10. Mice were vaccinated with the same bacterin and were subsequently allotted to 60 exposure groups which were exposed to 60 strains of E rhusiopathiae, comprising 10 strains each of serotypes 1, 2, 4, 9, 10, and 11. Response to challenge of immunity in swine was determined by the presence of clinical signs of acute generalized erysipelas; response in mice was determined by the quantal (live-dead) method. Vaccinated swine were as susceptible to the strain of serotype 10 as were nonvaccinated control swine, whereas vaccinated swine were immune and control swine were susceptible to the strains of serotypes 1 and 2. The strain of serotype 9 was not sufficiently virulent to induce acute generalized erysipelas, even in control swine. Arthritis was not prevented by vaccination, but its frequency and severity were less in vaccinated swine exposed to strains of serotype 1 or 2 than in those exposed to strains of serotype 9 or 10. Vaccinated mice were significantly (P less than 0.05) more susceptible to the strains of serotype 10 than to those of any other serotype tested.