Serum levels of TNF-beta and sTNF-R in patients with malignant bone tumours. To determine serum levels of TNF-beta and soluble TNF-R in patients with primary highly malignant bone tumours.Sera of 27 patients with highly malignant osteosarcoma and Ewing sarcoma were taken at the time of diagnosis and analysed by ELISA.Both TNF-beta and sTNF-R levels were lower in sera from osteosarcoma patients as compared to those from Ewing sarcoma. In patients with high-grade osteosarcoma, but not Ewing sarcoma, high levels of TNF-beta correlated with bad response to neoadjuvant chemotherapy.In patients with high-grade osteosarcoma TNF-beta levels seem to be of predictive value and both TNF-beta and sTNF-R seem to be of diagnostic value for differentiation between high-grade osteosarcoma and Ewing sarcoma.