['To determine the existence of a soluble signal, secreted from the human blastocyst embryo, that induces HOXA10 gene expression before cell-cell contact.', 'To analyze, by semiquantitative reverse transcriptase polymerase chain reaction (RT-PCR), cell-free media that had contained human embryos cultured to the blastocyst stage for a soluble molecule that induces HOXA10 expression in an endometrial epithelial cell line (Ishikawa).', 'Assisted reproduction technology program of Yale University, New Haven, Connecticut.', 'Patients undergoing intracytoplasmic sperm injection (ICSI) or in vitro fertilization (IVF) cycles. Treatment of Ishikawa cells with blastocyst-conditioned media.', 'Determination of HOXA10 gene expression.', 'We demonstrate that cell-free media that had contained human embryos cultured to the blastocyst stage contain a soluble molecule that induces HOXA10 expression in an endometrial epithelial cell line (Ishikawa). We found that hCG does not induce HOXA10 in Ishikawa cells.'] Does a soluble molecule secreted by human blastocysts modulate regulation of HOXA10 expression in an epithelial endometrial cell line?