Serum concentrations of sCD30 and sCD40L in patients with malignant bone tumours. The aim of this study was to evaluate serum levels of both soluble CD30 (sCD30) and soluble CD40 ligand (sCD40L) in patients with malignant bone tumours and to determine their ability to serve as serum markers. Sera of 31 patients were taken at the time of diagnosis, analysed by ELISA, and the results were correlated with clinical features and compared with healthy controls. Soluble CD30 and sCD40L levels were significantly higher in all patient groups than in the healthy controls. Soluble CD30 levels showed statistically significant differences between high malignant osteosarcoma and Ewing sarcoma (P = 0.015), whereas no statistically significant correlation was seen between different types of tumours and sCD40L levels. Soluble CD30 and sCD40L seem to be of diagnostic value in osteosarcoma and Ewing sarcoma.