Lead levels were measured in red blood cells and plasma of 75 pregnant women and their infants at delivery. No significant differences were found by comparing maternal and fetal values and a statistically significant positive correlation was evidenced, higher for plasma levels. The results suggest that the diffusible form of maternal lead in plasma influences the lead transferred to the fetus more directly. The highly significant correlation found between the maternal and fetal ratio of lead in plasma to lead in erythrocytes seems to be in favor of inborn factors influencing the equilibrium between the two compartments in which lead is distributed.