Murine L3T4 T cells freshly isolated from Peyer's Patch were fractionated based on differential adherence to Vicia villosa agglutinin (VVA). VVA adherent cells secreted IL-5, but not IL-2, after stimulation with Con A and IL-1. In striking contrast, VVA nonadherent PP L3T4 T cells secreted IL-2, but not IL-5, under the same conditions. In addition, supernatants from VVA adherent, but not from VVA nonadherent cells cultures, enhanced IgA secretion by LPS-stimulated splenic B cells to the same extent as purified IL-5. Thus, IL-5-producing T cells are present in PP in situ and may play an important role in the development of mucosal immunity. Further, differential adherence to VVA can be used to separate T cell populations that preferentially secrete IL-5 or IL-2.