The mucosal immune system is composed of distinct regional immune tissue (e.g., "GALT," gut-associated lymphoid tissue; "BALT," bronchus-associated lymphoid tissue; reproductive tract and breast tissue, and so forth) interconnected by trafficking of primed lymphocytes as a common "mucosa-associated lymphoid tissue," "MALT" (1). In addition, immune responses within MALT may occur independently of systemic immunity, with distinctive regulatory mechanisms and the induction of dimeric secretory IgA (SIgA) at the mucosal surface. As a result traditional methods for inducing systemic immunity may not induce significant SIgA, and techniques have been developed to deliver antigen directly to a mucosal surface in such a way as to induce immunity rather than immunological tolerance. The trafficking of primed B- and T-cells between mucosal sites, probably regulated by specific adhesion molecules, such as α4β7 integrin on lymphocytes and MAdCAM- on mucosal blood vessels (2), leads to dissemination of the mucosal immune response. One benefit of this, therefore, is that immunization of an accessible mucosal surface may induce an immune response at less accessible mucosal sites (such as the genital tract). Furthermore, by characterizing mucosa homing lymphocytes trafficking in the blood, it may be possible to indirectly study mucosal responses.