Endotoxin is abortifacient. Abortion may be due to maternal, fetal or combined endotoxemia. The present study was performed to evaluate if fetal rat endotoxemia was induced by maternal endotoxemia in late gestation. An intraperitoneal injection of smooth lipopolysaccharide (Escherichia coli LPS and Shigella flexneri LPS) or rough LPS (Rc mutant Escherichia coli LPS) induced Limulus activity in maternal plasma, but not fetal plasma. These results suggest that fetal rat endotoxemia is not induced during maternal endotoxemia. Thus, the abortion may not be due to fetal endotoxemia.