Recent evidence suggests that oxidative stress is involved in the pathophysiology of preeclampsia. Using immunohistochemistry and Western blotting, we investigated the oxidative stress- and redox-related molecules, such as 8-hydroxy-2'-deoxyguanosine (8-OHdG), 4-hydroxynonenal (4-HNE), thioredoxin (TRX) and redox factor-1 (ref-1) in the placenta in preeclampsia, intrauterine growth restriction (IUGR), preeclampsia + IUGR and in normal pregnancy. Using immunohistochemistry, the level of 8-OHdG was significantly higher in IUGR ( P=0.012) or preeclampsia + IUGR (P=0.0021) than in normal pregnancy, while TRX expression was significantly higher in preeclampsia (P=0.045), and ref-1 expression was significantly higher in preeclampsia (P=0.017), IUGR (P=0.016) and preeclampsia + IUGR (P=0.0038) than in normal pregnancy. The levels of 4-HNE did not differ significantly between either preeclampsia or IUGR and normal pregnancy. A significant positive correlation was observed between TRX and ref-1 expressions in both normal (rho=0.52) and complicated (rho=0.43) pregnancies. Using Western blotting, ref-1 expression tended to be higher in complicated pregnancies than in normal pregnancy (P=0.09). These results suggest that oxidative DNA damage is increased in IUGR and that redox function is enhanced in both preeclampsia and IUGR compared with normal pregnancy.