We have tested the hypothesis that the expression of interleukin-8 (IL-8) is increased in bronchial tissue and circulating leukocytes of atopic asthmatics, indicating a role for this chemokine in asthma. The concentration of IL-8 in its free form and complexed with IgG or IgA was measured by ELISA in bronchial tissue, serum, and lysates of freshly isolated peripheral blood mononuclear cells and granulocytes from subjects with mild or severe asthma and nonatopic nonasthmatic subjects. Serum ECP was measured by fluorescent enzyme immunoassay. Free IL-8 was detected in the sera (n = 44) and bronchial tissue (n = 9) of all subjects with severe atopic asthma, but it was undetectable in normal subjects and subjects with mild atopic asthma, suggesting that free IL-8 is a marker of severe asthma. A positive correlation between free IL-8 and serum ECP levels found in severe disease suggests that IL-8 is associated with eosinophil activation. Complexes of IL-8 with IgA and IgG were detected in all serum and tissue samples. However, the levels of the IL-8-IgA complex were increased in the bronchial mucosa in asthma, and in blood were related to disease activity. Together, these results point to upregulation of IL-8 production in asthma and the induction of IL-8 binding immunoglobulins of the IgA class in the inflamed mucosa. We suggest a proinflammatory role for these complexes in lung tissue.