Soluble interleukin-2 receptors (sIL-2R) are measurable in the sera of patients with ovarian cancer and several other benign and malignant diseases. However, the function of these sIL-2R is still unclear. Since high levels of sIL-2R are thought to be an indicator of an activated immune system we investigated the correlation of sIL-2R concentration and prognosis of ovarian cancer patients. sIL-2R measurement was performed on the preoperative sera of 130 patients with benign, and 119 patients with malignant ovarian tumors. The IMMULITE sIL-2R assay by DPC Biermann, Bad Nauheim, Germany was used. In ovarian cancer patients sIL-2R concentrations were significantly higher than in those with benign tumors. By defining the 95th percentile of the sIL-2R concentration distribution in patients with benign diseases as the cut-off (1200 U/ml) 35% of the ovarian cancer patients had elevated concentrations. Concentrations of sIL-2R increased with FIGO stage. FIGO-III patients with highly elevated sIL-2R concentrations tended to have better prognosis than those with sIL-2R levels within normal range in contrast to FIGO IV patients. Since sIL-2R concentrations indicate an immunological activation in ovarian cancer patients our data give hints of the possible role of sIL-2R in the assessment of the risk of recurrence in ovarian cancer patients.