Fifty 4-month old piglets were treated with immunomodulating Propionibacterium avidum KP-40 (PA) and/or immunized with live attenuated Erysipelothrix rhusiopathiae vaccine (Orvac). Four weeks after vaccination all animals were inoculated with viable Erysipelothrix rhusipathiae. The vaccine induced the appearance of high titers of specific IgG antibodies with peak values (1:115-1:200) three weeks after immunization. Administration of PA together with the vaccine did not influence antibody titers. Analysis of the course of experimental erysipelas infection in vaccinated and/or PA-treated swine revealed the prophylactic and beneficial effects of PA. PA-treated animals showed a significantly lower lethality rate than untreated controls and the course of the disease was considerably milder, with a shorter period of fever and a faster recovery. Vaccination provided good protection of swine against the development of erysipelas and therefore, the only significant difference in animals treated with PA applied together with the vaccine was a higher gain of body mass after infection.