Objective: To investigate whether the embryotoxic effect of peritoneal fluid (PF) from infertile women with mild endometriosis on mouse oocytes and embryos is associated with changes in embryonic epidermal growth factor (EGF), insulin-like growth factor-I (IGF-I), and their receptors. Design: Experimental animal study. Setting: University-based research laboratory. Animal(s): Adult ICR mice. Intervention(s): Peritoneal fluid was obtained from fertile women with no endometriosis (PF-NE) and infertile women with mild endometriosis (PF-E). In vitro fertilization was performed, and mouse two-cell stage embryos were cultured in human tubal fluid medium with or without PF. Main Outcome Measure(s): Rates of fertilization, cleavage, and blastulation. The embryonic EGF and IGF-I levels in culture medium were analyzed by enzyme-linked immunosorbent assay, and EGF receptor, IGF-I receptor, and phosphorylated extracellular signal-regulated protein kinases (p-ERK) expression was determined by immunofluorescence and confocal microscopy. Result(s): When oocytes and embryos were cultured in media with PF-E, the fertilization capability of oocytes and the development potential of embryos were decreased. The levels of embryonic EGF, IGF-I, and their receptors were increased. However, p-ERK of the postreceptor signal transduction pathway was down-regulated. Conclusion(s): Endometriotic PF may attenuate oocyte and embryo development by impairing embryonic growth factor/receptor/signal transduction, resulting in endometriotic infertility. © 2010 American Society for Reproductive Medicine.