To evaluate the effect of peritoneal fluid (PF) on preimplantation mouse embryo development and apoptosis, PF was obtained from women presenting with (n = 7) and without endometriosis (n = 7). Mouse embryos were cultured to the blastocyst stage in human tubal fluid medium alone (control) or 10% PF. Embryo development was assessed and the total cell number per embryo was determined by Hoechst 33258 staining. Allocation of inner cell mass and trophectoderm in blastocysts, and incidence of apoptosis were determined using confocal microscopy. The blastocyst development rate was significantly lower in the presence of 10% PF (P < 0.01). Total cell number and trophectoderm in blastocysts cultured in culture media alone was significantly higher than in the presence of PF (P = 0.034 and P = 0.01 respectively). A higher incidence of apoptosis was seen in blastocysts cultured in culture media alone, compared with those cultured in the presence of PF (P = 0.04). PF decreases the development of early mouse embryos to the blastocyst stage, as well as the incidence of apoptosis in the resulting mouse blastocysts. No difference was seen in the effect of PF from women with and without endometriosis on mouse embryo development and apoptosis.