Bacteria and their products play a key role in the etiology of periodontitis. They activate the host immunologic system which produces specific immunoglobulins (Ig). Mainly IgA, IgG and IgM are found in the oral environment, in the saliva IgA are present as secretory IgA. In case of periodontitis, the tissular destruction could be practically explained by spontaneous hypersensibility reactions which may contribute to deteriorate the periodontal tissues. Considering the complexity of the factors involved in periodontal inflammation (i.e. bacterial variety, difference of properties, patient's individuality, difference of analysis methods), the question of the exact role played by the antibodies still remains open.