Blood coagulation in vivo is initiated by factor VII (FVII) binding to its cellular receptor tissue factor (TF)(1-4). FVII is the only known ligand for TF, so it was expected that FVII-deficient embryos would have a similar phenotype to TF-deficient embryos, which have defective vitello-embryonic circulation and die around 9.5 days of gestation(5-8), Surprisingly, we find that FVII-deficient (FVII-/-) embryos developed normally, FVII-/- mice succumbed perinatally because of fatal haemorrhaging from normal blood vessels. At embryonic day 9.5, maternal-fetal transfer of FVII was undetectable and survival of embryos did not depend on TF-FVII-initiated fibrin formation. Thus, the TF-/- embryonic lethal and the FVII-/- survival-phenotypes suggest a role for TF during embryogenesis beyond fibrin formation.