Some studies have proposed exhaled breath condensate (EBC) as a noninvasive tool for monitoring airway inflammation in children. Moreover, atopic dermatitis (AD) has been considered a risk factor for the development of asthma. This study was designed to assess the EBC pH and the exhaled concentration of cytokines produced by T-helper (Th) 1, Th2, and T regulatory cells in asthmatic children and AD and to verify if their concentrations are affected by a short course of treatment with inhaled corticosteroids (ICS). We assessed the mean levels of pH, interferon (IFN) gamma, interleukin (IL)-4, and IL-10 in EBC of children with asthma (n=20) and AD (n=12) and healthy controls (n=20) by enzyme-linked immunosorbent assay (ELISA). Variations of pH and cytokine concentration in response to ICS (flunisolide, 500 microg/day, for 2 weeks), were also investigated in asthmatic patients. We found that the mean condensate pH value in patients with asthma and AD was significantly lower when compared with that of controls (6.9+/-0.2 and 7.0+/-0.2 versus 7.4+/-0.4; p<0.0001) and it significantly increased in asthmatic patients after treatment (7.2+/-0.2 versus 6.9+/-0.2; p=0.003). In addition, the IL-4/IFN-gamma ratio was significantly higher in children with asthma and in those with AD when compared with controls (9.72+/-2.00 and 9.70+/-2.0 versus 8.04+/-2.6; p<0.001) and that it decreased in asthmatic patients after ICS (6.4+/-5.4 versus 9.72+/-2.00; p<0.01). We observed that exhaled IL-10 levels were significantly higher in children with asthma compared with those of controls (18.8+/-8.9 versus 4.2+/-1.0; p<0.002). IL-10 did not significantly increase after treatment with steroids. No such finding was documented in children with AD. Our data suggest that EBC IL-10 levels are different in asthmatic patients compared with healthy children, but they are insensitive markers in monitoring therapy with ICS. Moreover, children with AD show an EBC pH and an exhaled pattern of Th2/Th1 cytokines similar to that of asthmatic patients.