Implantation is a complex process that requires the interaction of the blastocyst, and subsequently, that of the developing embryos with the endometrium. Several growth factors and cytokines are involved in implantation, but the details of their actions as related to the regulation of blastocyst implantation remain unclear. In the present study, the RT-PCR method was used to determine the gene expression of basic fibroblast growth factor (bFGF), keratinocyte growth factor (KGF), FGF receptor 1 (FGFR1), FGF receptor 2 (FGFR2), and KGF receptor (KGFR) in mouse embryos and in the stromal and epithelial cells of the uterine endometrium. Basic FGF and KGF mRNA were expressed in the endometrial cells, but were not expressed in the embryos. The mRNAs of receptors for bFGF and KGF were expressed in the blastocysts and in the in vitro implanting embryos, suggesting that bFGF and KGF may exert paracrine effects on blastocyst implantation. In this mouse model of blastocyst implantation, it was found that transforming growth factor alpha (TGF-alpha) at the concentrations of 1 ng/ml and 10 ng/ml significantly enhanced the blastocyst attachment and trophoblast spreading and increased trophoblast surface area. Relatively high concentrations of bFGF (100-500 ng/ml) significantly enhanced the rates of blastocyst attachment and of trophoblast spreading and promoted the expansion of the surface area of the implanting embryos. Unlike the rates of blastocyst attachment and trophoblast spreading, the surface area of the spreading embryos was significantly increased by addition of KGF (1-100 ng/ml). These results suggest that the bFGF and KGF derived from the endometrial cells exert paracrine effects on the process of implantation by stimulating trophoblast outgrowth through their cognate receptors.