Twenty-five patients with bronchial asthma and urticaria expressing hypersensitivity to ingested wheat were examined and compared with fourteen controls using the allergic autocytotoxicity assay (ACT). To establish a possible interaction between wheat antigen and antibody with OM-89 (immunostimulating fraction extracted from E. coli), peripheral WBC of the above individuals were tested in vitro. Preincubation with OM-89 and subsequent exposure toward wheat antigen in the direct ACT assay and antibody-dependent ACT assay using specific wheat antibody were performed. A separate study of spontaneous ACT was conducted in which unprimed white blood cells were pre-incubated with OM-89 alone. Our results show that OM-89 exerted its most potent inhibitory activity in the antibody-dependent ACT assay when the wheat antigen-antibody test system was used. Only borderline inhibition of the direct ACT response was observed, while OM-89 did not exert any effect on spontaneous ACT. This observation may be of importance in future clinical trials since patients sensitive to wheat with high antibody levels toward this common ingestant antigen may benefit from oral therapy with OM-89.