Levamisole (2, 3, 5, 6-tetrahydro-6-phenylimidazole 2,1-b thiazole) is a well-known nonspecific stimulator of host defence mechanisms. In previous investigations, we have found that levamisole acts on cell-mediated immunity in challenge-induced porcine postweaning colibacillosis (PWC). We assume that levamisole could also act synergistically on humoural immune response when applied as an adjuvant with vaccine candidate strains for oral immunization of weaned pigs against PWC. The influence of levamisole in combination with experimental F4ac+ nonenterotoxigenic Escherichia coli (non-ETEC) vacinal strain on proliferation of IgA+ cells was examined in 4-week-old weaned pigs experimentally infected with ETEC. We have performed identification and morphometric quantification of the plasma cell phenotype within jejunal/ileal mucosa. Plasma cells were identified by immunohistochemistry with monoclonal anti-IgA antibodies and quantifying by use of digital image analysis. Quantification of IgA+ cells from levamisole-primed vaccinated and challenge-infected weaned pigs showed significantly increased number (P < 0.05 for both jejunum and ileum) compared with those observed in unprimed vaccinated/challenge-infected controls. It is suggested from these results that levamisole may contribute in initiation of local humoural immune response to enteric pathogens, such as enterotoxigenic E. coli.