Fever, a fall in the plasma level of iron (Fe), and rises in the levels of certain plasma glycoproteins (indexed by protein-bound-N-acetylneuraminic acid [NANA]) normally occur during infection; they are thought to be mutually enhancing in host defense. It has been reported that fever is suppressed at full term of pregnancy; however, it is not known whether the blood chemical changes are similarly affected. Also, the mechanism for the suppression of fever is controversial. Since uteroplacental blood flow is at its maximum near term, competition between the demands of the fetoplacental unit and c·thermoregulatory effectors might result in underperfusion of thermogenic tissues and therefore provide a basis for the lack of fever. To examine these questions, the changes in colonic temperature (T(co)) and regional blood flow induced by Salmonella enteriditis endotoxin (LPS, 2 μg/kg iv) were compared in conscious nonpregnant and 30-day-pregnant rabbits 35 min after injection, using 15-μm radiolabeled microspheres. In different rabbits, the effects of LPS on T(co) and plasma Fe and NANA levels were measured before mating and at term. LPS induced fevers similar in heights and courses in both nonpregnant and full-term-pregnant rabbits. It caused decreases in the blood flows to brain, tongue, mammary gland, small intestine, and ear and increases in the blood flows to masseter muscle, bone, liver (hepatic artery), and left ventricle; blood flows to the kidneys, spleen, right ventricle, ovaries, and myometrium did not change. There were no significant differences in these vascular responses between nonpregnant and 30-day-pregnant rabbits, except a 28% reduction in the blood flow to the placentas. Plasma NANA responses to LPS were similar before and at term of pregnancy. Plasma Fe levels were lower and decreased less after LPS at term than before mating. These results indicate that neither fever nor its associated blood chemical changes are suppressed in rabbits at term of pregnancy. Similarly, the changes in regional blood flow that occur during fever onset are not different in term-pregnant and nonpregnant rabbits.