This report describes the use of cell mediated immunity to improve specificity of current diagnosis for Brucella suis. Diagnosis is problematic due to cross reactions that lead to false positive serological reactions (FPSR) in the standard diagnostic tests. A common cause of this cross reactivity is infection with the organism Yersinia enterocolitica O:9. Gottingen mini-pigs were experimentally infected with B. suis biovar I field strain or Y. enterocolitica serotype O:9 biotype 3. Infection was followed for 70 days. During this time whole blood stimulation assays were set up using Brucella specific antigen. IFNgamma was measured in the supernatants (SN) from these assays by ELISA. Concurrent standard serological tests were carried out. The results indicate that the IFNgamma assay is specifically able to distinguish Y. enterocolitica O:9 infection from a B. suis infection in experimentally infected mini-pigs. These results represent an improvement in diagnostic specificity compared to currently used serological tests. Thus suggesting that in a surveillance setting this test could be applied as a confirmatory test in the face of FPSR.