We characterized the tumorigenic and metastatic potential of a poorly differentiated, non-CEA-producing colon cancer cell line, MIP-101, after injection at different sites in athymic mice. After subcutaneous and intrasplenic injection tumor grew locally in 100 and 50%, respectively, but no metastases were found, even after intravenous injection. Intraperitoneal implantation, however, resulted in a high tumor take (10/10) and subsequent liver colonization (8/10 mice). Exogenous CEA prior to intrasplenic injection induced metastasis in 7/8 mice (in 2 mice to the liver and in 5 mice to the lung). Intrasplenic injection of CX-1, a good CEA producer, resulted in hepatic metastases in 100% of the animals. These data suggest a direct or indirect role of CEA in the metastatic process. We conclude that MIP-101 has a high tumorigenic and invasive potential but a low metastatic proclivity, except when grown in the peritoneum, and that pretreatment of tumor-bearing animals with CEA affects the metastatic proclivity.