Description: Three groups of 20 mice were inoculated subcutaneously once, twice or three times, respectively, with 109 colony forming units of Porphyromonas levii at 3, 5 and 7 weeks of age. Four mice were inoculated with saline and used as negative controls. An ELISA test was developed and used to assess the humoral reaction of mice to P. levii. Antibodies were present after the first inoculation and increased steeply after the second. The third inoculation had no significant effect on antibodies titers. These results indicate that P. levii induces a humoral immune response in mice in our model. Serum from mice challenged with a isolate of P. levii isolated from a case of Bovine Necrotic Vulvovaginitis was used to compare between different P. levii isolates from cows. Antibodies induced by this isolate cross-reacted with all the isolates studied and revealed a high degree of homology between these isolates