Peyer's patches (PPs) and/or mesenteric lymph nodes (MLNs) are thought to be essential for immunoglobulin A (IgA) production. We found that the severe IgA deficiency in lymphotoxin-deficient (LT^−/−) mice could be fully reversed by reconstitution with LT-expressing bone marrow, despite the absence of both LNs and PPs. The number of IgA precursors from LT^−/− mice was not reduced, and they were able to migrate into the lamina propria (LP) of wild-type mice but not of LTβR^−/− mice. Consistently, lymphoid tissue chemokines and adhesion molecules were reduced within the LP of LTα^−/− and LTβR^−/− mice. IgA deficiency in LTα^−/− mice was reversed by the transplantation of a segment of RAG-1 (recombination-activating gene 1)–deficient intestine, which confirmed the dispensability of the MLNs and PPs and the sufficiency of the LT-mediated gut microenvironment for IgA production.