The levels of relatedness among strains of Erysipelothrix serovar 7 isolated from dogs with endocarditis were estimated by performing DNA-DNA hybridization experiments with the type strains of Erysipelothrix rhusiopathiae and Erysipelothrix tonsillarum. All the canine strains exhibited more than 81% hybridization with the type strain of E. tonsillarum but less than 13% hybridization with the type strain of E. rhusiopathiae. Based on DNA-DNA hybridization results we confirmed that serovar 7 of the isolates from dogs with endocarditis were conclusively identified as E. tonsillarum. These results strongly indicate that some strains of genomic E. tonsillarum are a canine pathogen.