Increased levels of serum interleukin 6 (IL-6) are found in patients with lung cancer, and it has been shown that this is part of a systemic inflammatory response syndrome. This study was designed to measure IL-6 levels in bronchoalveolar lavage (BAL) fluid of patients with lung cancer and to describe the relationship of BAL fluid IL-6 to the known systemic increase in IL-6. Increased levels of BAL fluid IL-6 can be found in patients with lung cancer as compared with patients with chronic obstructive pulmonary disease who have acute infection (P = .007). In patients with cancer, no correlation between BAL fluid IL-6 and serum IL-6 was found (P = .8). BAL fluid IL-6 did not correlate with the number of lymphocytes or macrophages found in this fluid. BAL fluid IL-6 does not correlate with tumor size. Although serum IL-6 was higher in patients with extensive stage small cell lung cancer as compared with levels in patients with limited stage disease (P = .06), their corresponding BAL fluid levels were not different (P = .9). Serum IL-6 correlated with other acute phase reactants. This study thus demonstrates the feasibility of utilizing BAL fluid analysis for local cytokine/tumor marker production in lung carcinoma. It also shows that a local increase in IL-6 in the BAL fluid is independent of the systemic inflammatory response syndrome, whereas the serum increase in IL-6 is part of this syndrome.