Lipopolysaccharide (LPS) administration has been known to cause murine fetal death for over 50 years, but the responsible mechanism(s) remains unclear. We used the LPS-hyporesponsive murine strain, C3H/HeJ, to 1) establish whether LPS-induced fetal death is due to a maternal or fetal response to LPS and 2) to investigate the involvement of tumor necrosis factor alpha (TNF alpha) in fetal death caused by LPS. C3H/HeJ (LPS-hyporesponsive) or C3H/HeN (LPS-responsive) females were mated with C57B1/6 or C3H/HeN males (both LPS-responsive). Administration of 10 micrograms LPS caused fetal death in C3H/HeN mothers. However, up to 1000 micrograms LPS did not result in the death of LPS-responsive fetuses when administered to C3H/HeJ mothers. Systemic administration of TNF alpha was able to cause fetal death in both C3H/HeN and C3H/HeJ strains of mice. Pretreatment of pregnant C3H/HeN mice with anti-TNF alpha antibodies significantly reduced fetal death caused by LPS administration. The administration of a sublethal dose of TNF alpha plus 10 micrograms LPS to pregnant C3H/HeJ mice restored abortifacient activity. These results indicate that LPS-induced fetal death is due to a maternal response as opposed to a direct fetal response to LPS and that TNF alpha appears to be an important mediator of fetal death caused by LPS.