The evaluation of breath condensate (BC) composition is a new, non-invasive method studying inflammation processes in several respiratory diseases. Among many inflammation markers, hydrogen peroxide (H2O2) is the most common one, and its increased level was found in BC of cystic fibrosis and asthma patients. As in children's asthma, H2O2 is present and could correlates with the severity of the disease. The aim of our study was to check whether there exist differences between levels of H2O2 in children with allergic and non-allergic asthma. 83 allergic and 33 non-allergic children with mild asthma (50 girls and 66 boys, aged 7-17 years) were included in the study. All patients were clinically stable and used inhaled corticosteroids daily, and an inhaled bronchodilator on demand. Exhaled BC was obtained by spontaneously tidal volume breathing with EcoScreen (Jaeger, Germany). The content of H2O2 in the BC was measured spectrofluorometrically (homovanillic acid method). All subjects underwent flow-volume measurements immediately after collection of the condensate. Lung function in asthmatic allergic and non-allergic children showed near normal values and did not differ between groups. In the allergic group, the median H2O2 level in the expired condensate was 0.238 (0-1.86) microM, and in non-allergic 0.192 (0-0.78) microM (p > 0.05). We conclude that hydrogen peroxide in exhaled breath condensate of children with stable mild asthma does not differ significantly in allergic and non-allergic children and activity of airway inflammation seems to independent on allergic status of patients.