Probiotic lactobacilli have been proposed as a potential oral bacteriotherapeutic means of modulating immune phenotype expression in vivo, via their ability to promote cytokine production. This study investigated the ability of a known interferon (IFN)gamma-promoting probiotic (Lactobacillus rhamnosus HNOOI) to modulate cytokine production in mice expressing an on-going Th2-type immune response. BALB/c mice were primed to ovalbumin in alum adjuvant to invoke antigen-specific Th2 cytokine-secreting cell populations. Mice that were fed Lb. rhamnosus HN001 during antigen sensitization produced higher levels of lymphocyte-derived IFNgamma, but also interleukin (IL)-4 and IL-5, in comparison to control animals. Although HN001 was additionally shown to induce pro-IFNgamma monokine (IL-12, IL-18) secretion in macrophages in vitro, its ability to invoke mixed lymphocyte cytokine production during an on-going Th2-type immune response in vivo suggests that this probiotic is a general immunostimulatory agent, in contrast to the pro-Th1/anti-Th2 immunoregulation reported for some strains of IFNgamma-promoting lactobacilli.