BACKGROUND In asthmatic inflammation, TH2 cells play an important role. TH2 cells specifically secrete cytokines like IL-4 and IL-5. IL-4 stimulates IgE production and IL-5 is involved in hemopoiesis, chemotaxis, priming and activation of eosinophils. IFNgamma, produced by TH1 cells, has an inhibitory action on IgE production. OBJECTIVE To investigate the TH1/TH2-cell pattern in the cytokine production of peripheral blood of asthmatic children. We determined IL-4, IFNgamma and IL-5 in serum and in supernatants of unstimulated and stimulated (24 h with Concanavaline A) cultures of peripheral blood mononuclear cells (PBMCs) in 22 children with moderate asthma (mean age 9.3 years) and in 17 healthy controls (mean age 10.3 years). All children visited the out-patient department (OPD) where history taking, physical examination and blood sampling took place. Children younger than 8 years of age performed symptom and peak flow registration during 1 week after the visit to the OPD. RESULTS The number of eosinophils were significantly higher in children with asthma, compared with healthy controls. The concentration of IFNgamma in supernatants of cultures of stimulated PBMCs was significantly lower and the ratio of IL-4/IFNgamma was significantly higher in children with asthma compared with healthy controls. The FEV1 was directly and IgE was inversely related to the concentration of IFNgamma in supernatants of cultures of stimulated PBMCs. CONCLUSIONS IFNgamma may play an important role in the pathophysiology of childhood atopic asthma.