Recent studies suggest that steroid effects on uterine cell proliferation may be moderated by polypeptide growth factors. We now provide evidence that high affinity fibroblast growth factor (FGF) receptors are present temporally and spatially in the pregnant rat uterus (days 4-6) to support the idea that basic FGF action occurs via binding to its high affinity FGF receptor 1 (FGFR1). Reverse transcription-polymerase chain amplification indicates that both the full-length transcript and an alternatively spliced messenger RNA are present in the uterus. Western immunoblot analysis confirms that rat uterine membrane proteins contain two receptor isoforms, and these receptors bind basic FGF with high affinity and specificity. Immunolocalization of FGFR1 revealed receptor-positive cells in both the uterine stroma and epithelia on days 4-6 of pregnancy. However, the receptor was differentially localized in the disparate cell types. The nuclei of stromal cells were positive for FGFR1, whereas epithelial cell nuclei were negative. Together, these results suggest that FGF signal transduction in uterine stromal cells is mediated by activation of FGFR1.