This review focuses on three aspects of immunity at mucosal surfaces. The first is the origin of the commitment of mucosal surfaces to IgA synthesis and the possible role of isotype-specific regulatory T cells in this process. The role of T cells in switching from virgin, IgM-bearing cells to antigen-sensitive IgA-producing B cells is discussed in the context of recent developments in molecular biology, i.e., the possibility that the T cell regulates switching by providing a specific IgA recombinase. Second, the migratory patterns of cells from the gut mucosa to other mucosal sites are reviewed, and new data substantiating the migration of T cells in addition to B cells are presented. Third, the concept of oral tolerance is discussed, and the implications of the concomitant development of secretory immunity and systemic tolerance following enteric immunization are reviewed. New data are presented that suggest that although suppressor cells are present following oral immunization, prior treatment with agents such as cytoxan and colchicine, which eliminate splenic T suppressor cells, does not influence the induction of oral tolerance.