Previous studies have reported that cigarette smoking is a major source of exposure to cadmium (Cd). This study was carried out to determine the degree of exposure to Cd of pregnant women who smoke and to determine the degree of exposure to Cd of pregnant women who smoke and to determine the disposition of the Cd in the maternal-fetoplacental unit. Our data reveal that pregnant women who smoke expose themselves and their placentas to levels of Cd higher than those to which they would normally be exposed. The percentage increase in Cd due to smoking was 32% in the placenta and 59% in maternal blood; these increases are statistically significant. The mean levels of Cd in maternal blood, cord blood, and placental tissues of pregnant women who smoked were all higher than the mean levels of Cd in the same tissues and blood of pregnant women who did not smoke. In addition, the levels of Cd in the maternal blood of smokers were significantly higher than levels of Cd in the cord blood of their infants; this relationship was not found in nonsmokers. On the basis of the Cd data on cord blood and placental tissues, the fetuses found in nonsmokers. On the basis of the Cd data on cord blood and placental tissues, the fetuses of pregnant women who smoke apparently receive very little additional exposure to Cd; however, this does not lessen concern for the fetus. The presently reported increase in exposure to Cd of pregnant women due to smoking must be viewed as undesirable because Cd has been shown to alter placental function in animals, and because Cd has no known biologic function.