Historically, osteosarcoma has been a problematic metastatic disease, with 40-80% of patients developing pulmonary metastasis after primary tumor resection. Recent treatment advancements have reduced the occurrence of metastatic lesions to less than 30%. Using attenuated Salmonella typhimurium, we previously demonstrated regression in tumor burden in murine solid tumor and metastatic models. We established a murine model for metastatic osteosarcoma to determine the effect of treatment with a single oral dose of attenuated S. typhimurium with (SalpIL2) and without (Sal-NG) a gene for a truncated human interleukin-2. Female balb/c mice were administered 2 x 10(5) (ATCC K7M2) osteosarcoma cells via tail vein injection from culture and treated by oral gavage of Salmonella species 3 days later. Mice were harvested for splenic lymphocytes and tumor enumeration by intratracheal injection with India ink 21 days after injection. Treatment with attenuated SalpIL2 reduced pulmonary metastases in number and volume compared to saline controls. Furthermore, splenic natural killer cell populations were increased 93% with SalpIL2 and 114% with Sal-NG compared to nontreated groups. This pulmonary metastasis model demonstrates attenuated Salmonella typhimurium with human interleukin-2 reduced metastatic osteosarcoma in mice and confirm the need for further investigation into the immunologic properties of SalpIL2 as a possible treatment for metastatic osteosarcoma.