It has been shown that interleukin 8 (IL-8) is increased in bronchoalveolar lavage fluid (BALF) of patients with idiopathic pulmonary fibrosis (IPF) and there is increasing evidence that it is involved in the pathogenesis of this disease. To date, no data are available as to whether IL-8 is elevated in sera of IPF patients. We obtained sera from 42 patients with IPF and 20 healthy controls at time of BAL. From 20 of 42 patients with IPF and 12 of 20 controls BALF was available, enabling us to measure IL-8 in serum and BALF of the same time point. IL-8 was significantly elevated in serum (54.7 +/- 7.5 pg/ml, p < 0.0001) and BALF (715.7 +/- 112.4 pg/ml, p < 0.0001) of patients with IPF compared with controls (IL-8 in serum, 5.2 +/- 0.8 pg/ml; IL-8 in BALF, 67.3 +/- 9.7 pg/ml). We observed a significant positive correlation between IL-8 levels in BALF and percentage of BALF neutrophils (p < 0.001) and between serum IL-8 and BALF IL-8 levels (p < 0.005) in patients with IPF. Consequently, the serum IL-8 level correlated positively with the percentage of BAL neutrophils (p < 0.01), indicating that it may reflect the degree of neutrophilic alveolitis in IPF. Furthermore, the serum IL-8 level showed a negative correlation with important indicators of impairment of lung function (DL(CO), TLC, VC) and PaO2. In conclusion, we were able to demonstrate that the degree of neutrophilic alveolitis in IPF is reflected by increased serum levels of IL-8 and we suggest that the serological assessment of IL-8 may provide a useful parameter for clinicians in monitoring patients with IPF.