The effects of nicotine consumption on uteroplacental blood flow were studied in 20 pregnant women by means of placental blood flow measurements using indium-113m-transferrin. Smokers were found to have a higher rate of poor perfusion patterns than subjects of a control group. In addition, the number of cigarettes smoked daily was significantly correlated with the placental perfusion type. The mean birth weight of infants born by smokers was 250 g lower than in the control group. The results suggest that smoking during pregnancy may compromise uteroplacental blood flow and thus result in poor fetal development.