To evaluate serum tetranectin as a prognostic marker before first-line chemotherapy, serum levels were studied in 67 patients with metastatic breast cancer. In the Cox analyses, the relative risk (RR) for death of cancer varied with the cut-off level of serum tetranectin. A maximal RR of 5.0 was found for patients with serum tetranectin < or = 5.4 mg/l. The maximal RR of death for the other prognostic variables were multiple metastases 2.8, and for a poor performance status 2.0. Testing for the outcome, progressive disease, a maximal RR of 3.8 was found for patients with serum tetranectin < or = 5.3 mg/l, a maximal RR of 3.7 for multiple metastases and a maximal RR of 1.8 for a poor performance status. Significantly lower serum tetranectin values were found in patients with a poor treatment response compared to well responding patients. Serum tetranectrin seems to be useful as an additional prognostic factor in metastatic breast cancer.