The development of vaccines that would induce specific immune responses in the genital tract secretions would have far-reaching implications for not only the prevention of AIDS and sexually transmitted diseases but also the immunological control of fertility (4, 76, 88, 89, 123, 124, 149). Most of the currently studied vaccines utilize systemic routes of immunization which are of limited value for the prevention of mucosa-contracted diseases. The relative contribution of antigensensitized cells from PP or other inductive sites (e.g., rectal tonsils) to remote or adjacent effector sites (e.g., genital tract) as manifested by the appearance of corresponding S-IgA antibodies has not been studied extensively in humans despite its unquestionable practical importance. Exploration of immunization routes that are effective for induction of mucosal immune responses and that are based primarily on current knowledge of the origin of antibodies and of specific antibody-forming cells in mucosal tissues, together with novel antigen delivery systems (1, 76, 89, 130), is likely to reduce the incidence of many infectious diseases including AIDS and also reduce the cost of administration of such vaccines. © 1994 Plenum Publishing Corporation.