Mitomycin C treatment of 3-methylcholanthrene-induced syngeneic tumor cells in male mice of the highly inbred strain CBA/WEHI was a convenient and effective method for producing viable but nondividing tumor cells. A single sc injection of 1 x 10(6) mitomycin C-treated syngeneic tumor cells (MCT) induced a specific antitumor immune response that could mediate rejection of small subcutaneous tumor grafts and substantially inhibit growth of larger grafts in normal mice. The response was evident between 3 and 7 days after immunization and persisted for at least 120 days. Adoptive transfer experiments with peritoneal exudate cells from MCT-immunized mice indicated that a cellular basis for resistance was likely in the absence of a detectable humoral component. Administration of MCT to mice with established tumor grafts did not, however, affect tumor growth. Experiments with carrageenan and trypan blue showed that neither induction nor expression of cytotoxic effector cells in MCT-immunized mice was inhibited by these substances, though carrageenan and trypan blue augmented tumor growth in normal mice.