The purpose of these studies was to develop a metastatic osteosarcoma nude mouse model to evaluate the in vivo efficacy of new therapeutic compounds. Human SAOS-2 osteosarcoma cells (10(6) cells) were injected i.v. into nude mice. Cells isolated from a rare pulmonary metastases 6 months later were established (SAOS-LM1) in culture and re-injected. This procedure was repeated 5 additional times to produce the SAOS-LM6 cell line. Visible pulmonary nodules were present 8 weeks following i.v. injection of 10(6) SAOS-LM6 cells as compared to 17 weeks using SAOS-LM2 cells. Microscopic SAOS-LM6 pulmonary metastases were demonstrated at 6 weeks. Administration of adriamycin on week 9 resulted in regression of macroscopic SAOS-LM6 lung tumors. The ability of the model to be used to evaluate the effectiveness of a biologic agent against microscopic disease was also verified. It was concluded that this model can assess therapeutic efficacy and therefore, may have a role in investigating the potential of novel approaches aimed at eliminating pulmonary metastatic osteosarcoma.