The mechanism of airway eosinophilia during antigen-induced inflammation was investigated by measurement of eosinophil-active cytokines utilizing an eosinophil survival assay. In the first study, 4 patients with allergic rhinitis underwent segmental bronchoprovocation (SBP) with low, medium, and high doses of ragweed extract instilled into different bronchial subsegments; bronchoalveolar lavage (BAL) fluids were collected from each segment 12 min and 48 h after challenge. Eosinophil granule proteins and eosinophil survival activity were significantly elevated in the 48-h (late-phase) BAL fluids from these segments. Correlations were observed between the concentrations of eosinophil granule proteins and eosinophil survival activity (rs = 0.717 to 0.880, p < 0.001) in BAL fluids. Eosinophil survival activity was completely neutralized by anti-IL-5 monoclonal antibody in five of the seven 48-h samples tested representing three of the 4 patients. In the two remaining samples, eosinophil survival activity was only partially neutralized by either anti-IL-5 antibody or anti-granulocyte-macrophage colony-stimulating factor (GM-CSF) but was completely neutralized by anti-IL-5 and anti-GM-CSF in combination. Subsequently, in the second study, 10 patients with allergic rhinitis were challenged by SBP with ragweed extract. Eosinophil survival activity was significantly elevated in the 48-h BAL fluids; this activity was partially neutralized by anti-IL-5 antibody about (48%) and completely neutralized by the combination of anti-IL-5 and anti-GM-CSF antibodies. These findings suggest that the eosinophil survival activity in the late inflammatory lesions following SBP with allergen is mainly associated with IL-5, with small contributions from GM-CSF.(ABSTRACT TRUNCATED AT 250 WORDS)