Brucellosis is still a critical public health problem in many countries around the world. In humans, the infection is mainly acquired through the ingestion of milk-derived products from infected cattle. After the penetration of the bacteria in the body, several serum components are activated, and the immediate consequence is the attraction of phagocytic cells. The evolution of the disease often courses to a long lasting form, with frequent relapses. This appears to be due to the capability of Brucella's of surviving and, even more, multiplying within the mononuclear phagocytic cells. First, the intracellular location protects the bacteria from the effect of antibiotics. On the other hand, several studies have shown alterations in the phagocytic function. In some cases, the defects in phagocytosis are intrinsic to the host. However, Brucella organisms also display many mechanisms to evade the intracellular killing, which appears to be the reason for the success of the bacterium in dwelling within macrophages.