The mutagenic effects of Trp-P-1, Trp-P-2, Glu-P-1, Glu-P-2, Lys-P-1, MeA alpha C, A alpha C, MeIQ and IQ on Chinese hamster V79 cells with or without X-irradiated Syrian hamster embryo cells were examined. Of these products, only Trp-P-2 and Lys-P-1 induced ouabain-resistant mutants of Chinese hamster V79 cells in a dose-related fashion; X-irradiated Syrian hamster embryo cells were required for the mutagenicity of Lys-P-1, but not for that of Trp-P-2. None of the other pyrolysis products examined was mutagenic with or without X-irradiated Syrian hamster embryo cells.