Interleukin-8 (IL-8) belongs to the family of chemotactic cytokines and has been shown to activate neutrophils in vitro and in vivo. In this study, we measured IL-8 concentration in the serum of patients with pulmonary emphysema or bronchial asthma. IL-8 concentration in serum of emphysema patients was significantly higher than in asthmatics; in emphysema patients it was significantly correlated with the smoking index and the annual decrease of FEV1.0. In asthmatics IL-8 concentration was below the level of detection, but was markedly increased during exacerbation of asthma. Our findings suggest that IL-8 may be one of the causal factors in these diseases.