A syngeneic tumor model system with the RAW117 lymphosarcoma cell line was developed for use in investigations of host and tumor cell properties associated with an enhanced state of malignancy. This BALB/c mouse model was found to be similar to human lymphosarcoma in that liver and spleen were the major organs involved. Sequential in vivo selections were performed by iv tumor cell inoculation, removal of resulting solid liver tumor nodules for growth in vitro, and reinjection of the cultured cells iv. After ten such sequential selections for implantation, invasion, survival, and growth in liver, a lymphosarcoma cell line was obtained (RAW 117-H10) that formed approximately 200-fold more gross liver tumor nodules than did the parental tumor cell line in comparative biologic assays and displayed enhanced malignant properties when monitored by time of host death. Very few lung nodules or tumors were present at other sites with either the parental or any of the selected RAW117 lines, which confirms previous reports in which in vivo sequential selection yielded stable cell lines with preferential tumor colonization at specific sites.