The multifunctional cytokine interleukin-6 (IL-6) is produced by epithelial and mononuclear cells as well as by ovarian carcinoma cells. A prospective study was initiated to evaluate the clinical significance of systemic and local measurements of IL-6 concentrations in 67 patients with ovarian tumors. Eighteen patients who underwent laparotomy for ovarian carcinoma showed elevated levels of IL-6 in the serum as well as in the peritoneal cavity in comparison to patients with benign ovarian tumors. Furthermore, patients with advanced ovarian cancer, according to Figo-Stages III/IV, demonstrated higher IL-6 levels in the serum and ascites, respectively, than patients with Figo-Stages I/II reflecting low tumor burden. The results of the study suggest that IL-6 plays a key role in tumor-host interaction, particularly, in the possible facilitated spread of ovarian cancer cells.