Visfatin is a 56 kDa protein that is overexpressed in pregnant women. Like insulin, 2 nM visfatin induced GLUT 4 translocation from the cytosolic fraction to the membrane in 3T3-L1 cells. We have previously reported that visfatin induces glucose uptake into 3T3-L1 cells. These two actions define visfatin as an insulinomimetic. Three estrogens are elevated in pregnancy. Estradiol, the predominant estrogen, estriol, produced by the fetal liver and the pro-estrogen progesterone are all higher during pregnancy than in nonparous women. 3T3-L1 cells were treated with 150 ng/ml estriol, 16 ng/ml estradiol or 190 ng/ml progesterone to reflect the circulating concentrations of these steroids during pregnancy. Estriol treatment produced a 2.5-fold increase in visfatin gene expression. Estradiol and progesterone had small but insignificant effects on visfatin gene expression. In a second experiment, cells were treated with a combination of all three steroids together at the same concentrations listed above. The combination treatment produced a 13-fold increase in visfatin gene expression. These data suggest that the estriol, estradiol and progesterone exert a synergistic effect on visfatin gene expression. Taken together these data suggest that visfatin may play a physiological role during pregnancy. Since visfatin potently and efficaciously induced GLUT 4 translocation in a cell culture model, any hypothetical role for visfatin in pregnancy should include the possibility that it may play a role in maternal/fetal glucose metabolism or distribution. Two possibilities present: either maternal visfatin is overexpressed as a protective response in the pregnant female to compensate for the insulin resistance that often accompanies pregnancy or the excess visfatin is a compensatory response to ensure adequate glucose delivery to the growing fetus.