Intratumor chemotherapy with the use of mitomycin C and/or immunotherapy caused regression of line 10 carcinomas in strain 2 guinea pigs and resulted in development of tumor-specific immunity. The immunotherapeutic preparation consisted of oil-in-water emulsions containing Mycobacterium cell walls or residues of cell walls termed cell wall skeletons. The latter preparations were combined with trehalose dimycolate, which was isolated by microparticulate chromatography from whole cells of mycobacteria. Reducing mitomycin C to a single intratumor injection of 50 microgram produced little necrotizing effect and a mean tumor regression rate of 17%. Intratumor immunotherapy 1 day after treatment with 50 microgram of mitomycin C resulted in regression of 90% of the treated tumors as compared to mean regression rates of 30 to 50% for immunotherapy alone. In addition, chemoimmunotherapy was more effective than either chemotherapy or immunotherapy alone in producing regression of relatively large, as well as smaller, tumors.