Human epididymis 4 (HE-4) protein has been proposed as a tumor marker for lung and ovarian cancer. This study was designed to measure HE-4 levels in bronchial aspiration fluid (BAF) of patients with lung cancer and to describe the relationship of BAF HE-4 with known systemic increase in serum HE-4 levels. Sixty-four patients with lung cancer, 38 with benign lung disease and 19 healthy subjects, were enrolled in our study. The BAF was obtained during routine bronchoscopic procedure in patient groups. HE-4 levels in serum and BAF were measured with the commercially available kit by an enzyme-linked immunosorbent assay. Serum HE-4 levels were significantly higher in patients with lung cancer group (204.2 +/- 22.9 pmol/L) than in benign lung disease group (135 +/- 26.9 pmol/L, p = 0.001) and healthy subjects (14.8 +/- 7.0 pmol/L, p < 0.0001). No significant difference was observed in terms of BAF HE-4 values in two patient groups. BAF HE-4 levels were significantly higher than those of serum levels in both patient groups (p < 0.0001). Serum HE-4 level was correlated with tumor stage (p = 0.001) and age (p < 0.0001) in the lung cancer group. The areas under the receiver operating characteristic (ROC) curve of serum HE-4 was 0.784 (95 % confidence interval (CI), 0.701-0.867) and that of BAF HE-4 was 0.496 (95 % CI, 0.382-0.610). This study shows that a systemic increase in serum of HE-4 is more prominent than a local increase of HE-4 (BAF), so this may suggest the feasibility of using serum instead of BAF samples for HE-4 measurements in lung cancer cases.