The purpose of this study was to determine whether cytotoxic chemotherapy influences the number and function of alveolar macrophages (AM) in patients with lung cancer. AM were obtained by bronchoalveolar lavage from 24 patients with lung cancer and 17 control patients. The functional integrity of AM was determined by their ability to produce interleukin-1 beta (IL-1 beta) and interleukin-1 receptor antagonist (IL-1ra) before and after platinum-containing systemic chemotherapy. The productions of IL-1 beta and IL-1ra were quantitated by enzyme immunoassays. The proportions of multinucleated cells among AM were significantly decreased after systemic chemotherapy in lung cancer patients. No significant difference in spontaneous and lipopolysaccharide (LPS)-stimulated IL-1 beta or IL-1ra production by AM was observed between lung cancer patients and control patients. Significant increase of IL-1 beta and significant decrease of IL-1ra production by AM were demonstrated in patients with small cell lung cancer who experienced response to systemic chemotherapy. These results suggest that systemic chemotherapy may influence functional roles of AM in the lung, and consideration of influence of systemic chemotherapy on host functions is important in cancer treatment.