Leukocyte zinc levels were significantly higher in normal pregnant women than in normal controls (p less than 0.001). There were inverse correlations between plasma zinc and leukocyte zinc (r = -0.76, p less than 0.001) and between plasma zinc and placental zinc (r = -0.88, p less than 0.0001) in normal pregnancies. When compared with infants borne by some pre-eclamptic subjects, there were significant increases in cord plasma zinc of infants borne by normal pregnant subjects (p less than 0.001). Plasma zinc concentrations were lower in normal pregnant subjects and in pre-eclamptics who gave birth to infants with normal birthweight than in pre-eclamptics who delivered infants with lower birthweight (p less than 0.005). When compared with normal pregnant women and pre-eclamptics who gave birth to infants with normal birthweight, total plasma estrogens were decreased in pre-eclamptics who delivered infants with lower birthweights (p less than 0.001). The data from this study suggest that in human pregnancy, zinc and estrogens compete for common binding sites on the plasma proteins and zinc plays an important role in the course and eventual outcome of human pregnancy.