BACKGROUND AND OBJECTIVE: Previous studies, during acute asthma exacerbations, have suggested roles for the Th2 cytokines in promoting airway inflammation in asthma patients. We assessed mediators of airway inflammation during the chronic asymptomatic phase of asthma. METHOD: Nine nonatopic asthma (NAA) patients, 15 atopic asthma (AA) patients, 15 atopic controls (AC), and 21 normal controls (NC) underwent sputum induction in asymptomatic phase. Sputum total cell counts and differentials were determined. Levels of the cytokines, IL-4, IL-5, GM-CSF, IFN-gamma were measured by ELISA. RESULT: NAA and AA patients showed a higher percentage of sputum eosinophils compared to AC (P<0.001, P<0.01, respectively) and NC (P<0.001); furthermore, NAA patients showed higher percentage of sputum eosinophils and total eosinophils compared to AA (P<0.01, P=0.001, respectively). No differences were observed in the sputum levels of IL-4 and IL-5 among the four groups. In contrast, the IFN-gamma levels were higher in NAA (P<0.001) and AA (P<0.001) patients compared to AC and NC. Interestingly, the GM-CSF levels were higher in AA patients compared to AC (P=0.01) or NC (P<0.001). In NAA, AA, and AC patients, the percentage of sputum eosinophils and total eosonphils correlated positively with the levels of IFN-gamma (Rs=0.643 and P<0.001, Rs=0.580 and P<0.001), GM-CSF (Rs=0.459 and P<0.01, Rs=0.394 and P<0.05), but not with the IL-5 levels. CONCLUSIONS: The baseline airway inflammation of asthma, irrespective of an atopic or nonatopic diathesis, is characterized by eosinophilic inflammation and a Th1 cytokine, IFN-gamma. GM-CSF, instead of IL-5 may have a role in airway eosinophilia during the chronic phase of asthma.