The aim of this work was a review of literature with regard to the mucosal immunity, the oral vaccines and the bacterial lysates. The Gut Associated Lymphoid Tissue (GALT) include effector and inductive sites and is constituted by organized and diffuse tissues. GALT defends the integrity of the gut, inhibits the development of allergy and autoimmunity and induce a mucosal and systemic immune response against enteric antigens. Bacterial lysates are innocuous and can reduce the frequency and the seriousness of diarrhoea, mucosal infections and diverticulitis; they induce the production and the biologic activity of secretory IgA and cytokines. The DNA vaccines are able to induce a strong immune response; the oral vaccines formulated with bacterial adhesins can inhibit the entry of pathogens and oral antigens across the gut. The use of adjuvants can amplify the activity of the oral vaccines; an objective of the research is the discovery of potent adjuvants without remarkable toxicity.