The production of the five classes of immunoglobulins represents the highest grade of the various system of defence the man puts in act against the microbial attack. So bacteria fight in several levels across the different stages of human antibodies synthesis processes and action, trying for cancelling the effect. Therefore, a more exact definition of the mechanisms of bacterial actions against human immunoglobulins would permit us to intervene in a more efficacious way in favour of defence powers of the human organism. In this way we could improve the knowledge of the bacterial damage process, increase the means of human immunization, and our therapy attempts. We analyzed therefore in this study the different defence mechanisms that bacteria use against human immunoglobulins. Bacteria can avoid "a priori" or divert antibodies formation, by synthesis of surface structural identical to components of the host. Bacteria can stop or hinder transmission of antigenic message working against the phagocytosis mechanisms. Bacteria can stop or lessen antibodies synthesis process. Bacteria can avoid specific contact with antibodies, especially, by masking the microbial surface. Bacteria can change their superficial structures to avoid antibodies action. Bacteria can destroy antibodies by synthesis of protease activity capable of hydrolyzing globulins.