Serum concentrations of APO-1/Fas and interleukin-1beta-converting enzyme in osteosarcoma correlate with response to chemotherapy. Cytotoxic drugs used in neoadjuvant chemotherapy may exert their effect by activation of apoptosis. Both APO-1/Fas and Interleukin-1beta-converting (ICE)/caspase-1 are believed to act as mediators of apoptotic cell death.The sera of 21 patients with high-grade osteosarcoma were tested at the time of diagnosis by ELISA and compared with clinical data.The mean APO-1 serum levels were 844 +/- 344 pg ml(-1) and the mean ICE serum levels were 212 pg ml(-1) +/- 155 pg ml(-1) for all patients. Furthermore, both serum levels were found to be statistically significantly higher in patients with good regression grades compared to those in patients with bad regression grades.In highly-malignant osteosarcoma elevated serum levels of both APO-1 and ICE seem to be predictive of good response to chemotherapy.