It has been demonstrated that significant protection against YC8 lymphoma can be induced in mice preimmunized with normal DBA/2 spleen cells. The DBA/2 spleen cells used as an alloantigen share minor histocompatibility determinants with the YC8 tumor. Our observations showed that once tumor was present in vivo, the use of a potent tumor specific vaccine that can confer 100% protection to preimmunized animals, can help in increasing survival but can no longer produce high incidence of regression and cure. We have used this model to show that adoptive chemoimmunotherapy (ACIT) can be used to regress tumors in mice with large body burden of tumor and that combination of conditioning with ACIT appears to enhance the effectiveness of treatment. The nature of the immunity conferred by conditioned resistance might be due to cytotoxic T-lymphocytes.