Abstract Tumor-specific transplantation antigens were extracted from two methylcholanthrene-induced murine sarcomas. Administration of the soluble material to syngeneic hosts yielded immunoprotection against a challenge of supralethal numbers of tumor cells. The protective effect was only induced over a narrow dosage range; higher doses were ineffective. The engendered immune state could be overcome with larger numbers of cells in the tumor challenge. The restricted range of immunogenicity of soluble extracts in this experimental system cautions against premature clinical application of these materials as immunotherapeutic tools.