Virgin, pregnant and hormone prctreated rats were infused with endotoxin for 6 h. Pregnant rats revealed, in the endotoxin dose ranges employed, more glomerular involvement than virgin rats, indicating their higher susceptibility to disseminated intravascular coagulation (DIC). Pretreatment of virgin rats with estrogen and progesterone augmented the glomerular involvement of virgin rats, but glomerular fibrin deposition did not reach the high values of pregnant animals, except in the excessive dose ranges. It is concluded that a pseudopregnancy regimen augments DIC but that there are additional factors involved in the high susceptibility of pregnant animals. The platelet number decreases after endotoxin infusion similarly in all three groups. The hematocrit decreased more in the pregnant and hormone-treated rats than in the virgin group.