Alcohol use exceeding 3 to 5 daily drinks is associated with a 30% to 50% risk of delivering a child with fetal alcohol effects (FAE). FAE could be prevented if women were counseled and if they decreased their drinking. Therefore, we need sensitive and specific markers to detect alcohol abuse during pregnancy. We investigated whether acetaldehyde-hemoglobin adducts (Hb-Ach) could be such a marker. Using an antiserum specific for acetaldehyde-generated epitopes in proteins, we measured the levels of Hb-Ach from the red cells of 19 women visiting the outpatient department of pregnant alcohol abusers and from 14 nonpregnant controls. The pregnant women were carefully followed to receive personal antenatal care and intensive counseling on alcohol. Nevertheless, eight of the women delivered infants with FAE. The remaining 11 women had healthy infants, although only four of them stopped drinking totally. The highest concentrations of Hb-Ach were found from women who subsequently delivered children with FAE. When compared with the pregnant women abstaining from ethanol the Hb-Ach values were found to be elevated in five of eight (63%) of the women who gave birth to children with FAE, whereas only in two/seven (28%) of the mothers who despite drinking delivered healthy children. Hb-Ach measurements during pregnancy may prove to be useful to monitor the compliance of women withdrawing from alcohol and to distinguish the mothers at risk of affected offspring. The studies also support a pathophysiological role of acetaldehyde in producing ethanol-associated fetal injury.