Increased levels of interleukin-6 (IL-6) and interleukin-8 (IL-8) have been reported in various diseases, including lung cancer. The role of the soluble form of the IL-6 receptor (sIL-6R) remains to be explored. We therefore measured IL-6, IL-8 and sIL-6R in effusion fluid and blood serum of 10 lung cancer patients with carcinomatous pleurisy (5 men, 5 women, age 64.3 +/- 4.4 years) by enzyme-linked immunosorbent assays. Serum levels of healthy individuals served as control. Concentrations of sIL-6R were much higher in serum compared to pleural effusion fluids of tumor patients (25,698 +/- 1,993 vs. 9,438 +/- 1,407 pg/ml: p < 0.0001). In contrast, IL-6 and IL-8 were found at high concentrations in carcinomatous pleural effusions in comparison to serum (IL-6: 964 +/- 176 vs. 10.2 +/- 1.3 pg/ml, p < 0.0001; IL-8: 319 +/- 85 vs. 9.6 +/- 9.6 pg/ml, p < 0.0001). The serum concentrations of IL-6 were not significantly increased in lung cancer patients (10.2 +/- 1.3 pg/ml) in comparison to controls (7.3 +/- 1.0 pg/ml). IL-8 was detected in the serum of only 1 patient and in low levels in the serum of controls (8.0 +/- 1.5 pg/ml; all values are mean +/- SEM). We conclude from this study that decreased levels of sIL-6R, but increased levels of IL-6 and IL-8, are found in pleural effusion fluid of patients with lung cancer and carcinomatous pleurisy. The low sIL-6R levels in the presence of high IL-6 levels in pleural effusions and the high sIL-6R levels in the presence of low IL-6 levels in serum may suggest a downregulation of sIL-6R expression of sIL-6R shedding in the presence of excessive amounts of IL-6.