Interleukin-8 (IL-8) is a pleiotropic cytokine that has also been shown to exert effects relevant to cancer growth and progression. Cancer progression is believed to be contributed to by the ability of this cytokine to promote angiogenesis and mitogenic effects. As IL-8 production at the tumor site may determine elevated serum levels of this cytokine because of hematogenous leakage, it is conceivable that patients with high IL-8 serum levels may have tumors actively producing this cytokine. The aim of this study was, therefore, to assess IL-8 serum levels in 60 non-small cell lung cancer (NSCLC) patients undergoing chemotherapy and to correlate them with prognosis. IL-8 serum levels were found to be significantly elevated in cancer patients with respect to controls. Moreover, IL-8 serum levels were shown to be significantly increased in stage IV patients compared with stage III patients. When basal IL-8 serum levels in cancer patients were analyzed according to response to chemotherapy, responders were shown to have significantly lower IL-8 serum levels than nonresponders. On univariate analysis, the IL-8 serum level was included among the variables capable of affecting both overall survival (OS) and time to treatment failure (TTF). However, multivariate analysis failed to demonstrate an independent prognostic significance for IL-8 serum levels. In conclusion, this study showed that IL-8 serum levels were elevated in advanced NSCLC patients and correlated with both OS and TTF, but they were shown not to be an independent prognostic factor.