The distribution and the kinetics of potentiated antibody synthesis have been studied at the cellular level in rats infested with Nippostrongylus brasiliensis using the homologous adoptive cutaneous anaphylaxis technique. In animals immunized in the hind footpads with alum-absorbed ovalbumin 10 days prior to infestation with the parasite, the major sites of potentiated anti-ovalbumin homocytotropic antibody synthesis were the regional lymph nodes of the gut and the lungs. Peyer's patches were weakly active late in the response and the spleen produced considerable amounts of potentiated antibody. The regional lymph nodes of the ovalbumin immunization sites were the only organs in which specific homocytotropic antibody synthesis was detected in uninfested control rats. The kinetics of synthesis of the potentiated antibody by cells correlated well with the levels of anti-ovalbumin IgE antibodies in the sera of the infested rats. A traffic of cells secreting anti-ovalbumin homocytotropic antibody was detected in the thoracic duct lymph, but not the mesenteric lymph of immunized uninfested rats. After infestation, the mesenteric lymph also contained cells secreting potentiated antibody. The mesenteric lymph is a major route by which IgE and potentiated IgE antibodies reach the circulation in infested rats. The possible mechanisms responsible for the effects of the parasite on antibody secretion in distant lymphoid organs are discussed.