Insulin resistance increases during the normal course of pregnancy, and is considered an important cause of complications including gestational diabetes mellitus, pregnancy-induced hypertension and preeclampsia (PE). Adiponectin, an adipocyte-specific plasma protein, is thought to enhance insulin sensitivity; another adipocytokine, leptin, also is thought to promote insulin sensitivity. We determined peripheral blood concentrations of adiponectin and leptin in 40 healthy nonpregnant women with a body mass index (BMI)<25, 40 healthy pregnant women with prepregnancy BMI<25, and 15 PE patients with prepregnancy BMI<25. Serum adiponectin concentrations were lower in the healthy pregnant group than in the nonpregnant group (9.40+/-4.43 versus 13.15+/-6.69 microg/mL, p<0.01), but difference disappeared after correction for haematocrit. Serum leptin concentrations were high in the normal pregnant group after correction for haematocrit (10.08+/-6.58 versus 6.24+/-3.61 ng/mL, p<0.05). Corrected after haematocrit, serum adiponectin in PE patients was higher than healthy pregnant women at 28 to 40 gestational weeks (17.46+/-11.81 versus 9.33+/-4.47 microg/mL, p<0.01). Leptin in PE was higher than in the normal pregnant group (21.15+/-19.89 versus 11.77+/-6.25 ng/mL, p<0.05), also after correction for haematocrit. These results suggested a metabolic shift in normal pregnant women and PE patients mediated through adipocytokines.