The experiments reported here concern the characterization by techniques of in vitro cell-mediated immunity of the antigens induced by 5-(3,3' dimethyl-1-triazine)-imidazole-4-carboxamide (DTIC) on L1210, a chemically-induced lymphoma of DBA/2 mice (H-2d). This series of experiments with the DTIC-treated L1210 tumour show the presence of an 'H-2D'-like antigen which resembles the Dk gene product/s of the H-2k haplotype.