The goal of this study was to evaluate the in vitro Th1/Th2 cytokine response as well as proliferative response in M. catarrhalis antigen-stimulated PBMC from 14 atopic asthma children (AA) and 11 non-atopic children suffering from recurrent respiratory tract infections and bronchospastic symptoms (RRTI). Membrane (MA) and soluble (SA) antigens of M. catarrhalis induced PBMC to production of IFN-g but did not induce cells to secretion of IL-4 and IL-13. The production of IFN-&#947; after stimulation with both MA and SA was considerably higher than spontaneous ones within each group (AA and control, P<0.001; RRTI, P<0.01). Furthermore, proliferative response of PBMC following SA stimulation between 4- and 7-day of culture showed significant increase contrary to the MA stimulation in analogous time. PBMC from RRTI group secreted significantly less IFN-&#947; as compared with controls (MA, P<0.05; SA, P<0.001). Release of IL-4 and IL-13 by PBMC did not differ between the three groups. Concluding, the comparable productions of IFN-&#947; during stimulation of PBMC with MA and SA suggest, that apart from the former also the latter may have a strong impact on the Th1-type cytokine response. We proposed also that reduced IFN-&#947; in RRTI group may be one of important factors in non-effective defence mechanism.