Resistin is expressed in human placenta and has been postulated to play a role in regulating energy metabolism in pregnancy. However, changes in serum resistin levels in normal pregnancy and in the setting of pre-eclampsia are far from understood. The purpose of the present study was to clarify the alterations in serum resistin level in normal pregnancy and pre-eclampsia. Blood samples were taken from 28 healthy non-pregnant women, 27 women in the first, 26 in the second and 26 in the third trimesters of normal pregnancy and 25 women with pre-eclampsia. Serum resistin concentrations were determined by using an ELISA, and mean serum resistin levels were compared with one-way ANOVA. Serum resistin levels were not significantly different among non-pregnant women and women in the first and second trimesters of pregnancy (P>0.05 for all). Serum resistin was significantly elevated in the third trimester of normal pregnancy compared with non-pregnant women (P<0.01) and women in the first (P<0.001) and second (P<0.001) trimesters of pregnancy. Serum resistin level was significantly lower in women with pre-eclampsia than women in the third trimester of normal pregnancy (P<0.001), but was comparable with those of non-pregnant women and women in the first and second trimesters of pregnancy (P>0.05 for all). In conclusion, we found an increase in serum resistin in the third trimester of normal pregnancy, but this increase was not present in pre-eclampsia. We postulate that these associations may offer insight into the mechanisms of maternal adaptation to pregnancy and the pathogenesis of pre-eclampsia.