SaI is an A/J-derived (H-2K(k)D(d)) transplantable mouse fibrosarcoma that produces a solid tumor when inoculated subcutaneously, intradermally, or intramuscularly, and an ascites tumor when inoculated intraperitoneally into syngeneic mice. This unit describes the establishment of primary solid SaI/N tumor, the establishment of SaI ascites tumor, and the removal for sampling of in vivo-passaged SaI ascites tumor cells in mice.