Mesenteric node lymphocytes from mice that had been infected with the nematode Trichuris muris, and then boosted with adult worm excretory-secretory antigens were fused with myeloma cells to produce a panel of 9 monoclonal antibodies (MoAbs). Five of the MoAbs were of the IgA isotype. The antigen recognition profiles of these MoAbs were studied using SDS-PAGE and immunoblotting; three major profile patterns were identified. Five MoAbs recognized a major band in the MW range 43-48 kD; all recognized a range of antigens. Three MoAbs were used to localize antigens in the bodies of adult worms. Granules within the anterior stichocytes were recognized strongly, as was material within the eggs and pseudocoelom. Two MoAbs stained the cuticle. Although the phosphorylcholine (PC) determinants was widely distributed within worm tissues none of the MoAbs tested recognized PC. Passive transfer of immunity was achieved using two of the IgA monoclonals; no immunity was transferred by the IgM and IgG MoAbs used. The limited recognition profiles of these IgA MoAbs, and the ability to stain stichocyte granules, suggest that their protective activity results from an interaction with ES antigens.