In this report, we examine the cytotoxic effects of puerarin, an isoflavone compound, on the blastocyst stage of mouse embryos and subsequent embryonic attachment and outgrowth in vitro and in vivo implantation by embryo transfer. Mouse blastocysts were incubated in medium with or without puerarin (2.5, 5 or 10 microM) for 24h. Cell proliferation and growth was investigated by dual differential staining, apoptosis was analyzed by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL), and implantation and post-implantation development of embryos were measured by in vitro development analysis and in vivo embryo transfer, respectively. We found that blastocysts treated with 5 or 10 microM puerarin showed significant increases in apoptosis and significant decreases in total cell number. Interestingly, there was no significant difference of implantation success rate between puerarin-pretreated blastocysts and controls, but in vitro treatment with 5 or 10 microM puerarin was associated with increased resorption of post-implantation embryos and decreased fetal weight. Our results collectively indicate that in vitro exposure to puerarin induced apoptosis and after transfer to host mice retards early post-implantation development. The extent to which puerarin may have teratogenic potential in early human development is not yet known.