Brucella abortus is the intracellular bacterium that causes bovine brucellosis and a chronic human disease known as undulant fever. Interferon (IFN)-gamma plays critical roles in defending against intracellular bacterial infection. In this experiment, we demonstrated the difference in IFN-gamma production between the splenocytes of mice inoculated with outer membrane proteins (OMPs) of B. abortus and whole live bacteria. Our results showed that the OMP-inoculated group showed more IFN-gamma production than did the bacteria-infected group, suggesting that OMPs are candidates for the induction of immune response.