Mouse embryos were collected at the 2 cell or 8 cell stage. The embryos of each stage were exposed to 1 pM-10 nM 4-nitroquinoline-1-oxide (4-NQO) or 1 nM-10 microM N-methyl-nitro-nitrosoguanidine (MNNG) for 24 hr, and cultured to develop to blastocysts within clean medium. Since after exposure to 4-NQO, the appearance of early blastocysts and blastocysts were increased in exposure groups compared with controls, the growth to the 8 cell stage embryo (8-E) appeared to be late in development. Frequency of sister chromatid exchange (SCE) and mitotic index were increased with doses in the blastocysts (2-B) which derived from 2-E. There was little change in the SCE and mitotic index for blastocysts (8-B) which derived from the 8 cell stage embryo (8-E). Cessation of development in the 2 cell stage embryo (2-E) appeared in the 10 microM group during the period of exposure to MNNG. Development to the 8-E stage appeared to be slightly late in the other exposed groups. Thereafter at 48 hr after the initiation of culture, the exposed groups appeared to be more advanced in development than the controls. After this period, developmental rates to blastocysts were increased in the 10-100 nM groups. It appeared that the development of these groups was more advanced. In 2-B after exposure to MNNG, cell counts were dose-responsively increased in the 1 and 10 nM groups. The mitotic index in the 1 to 100 nM groups was higher than the controls.(ABSTRACT TRUNCATED AT 250 WORDS)