Cords, placentas, placental membranes, and maternal and fetal blood were collected from 249 women delivered in Columbia, Missouri (Region I). The same samples were obtained from 253 women delivered in Rolla, Missouri (Region II), near lead mining areas. The incidence of term pregnancies with early membrane rupture was 0.41% in Region I and 17% in Region II. The incidence of premature deliveries was 3% and 13.04% respectively. Lead concentration in blood and placental tissues of term pregnancies revealed no significant changes. In term with early membrane rupture, blood concentration of lead was higher, as was the case in placental tissues and cord. Lead concentration was highest in membrane tissues, in mug/100 grams (Regions I and II respectively): placenta, 6.0 +/- 0.01 and 7.0 +/- 0.03; cord, 11.0 +/- 0.34 and 12.0 +/- 0.18; membrane, 38.9 +/- 2.64 and 45.3 +/- 3.12. A high positive correlation (r = 0.2941) between lead concentration in maternal and fetal blood existed. Both were significantly (P less than 0.01) higher in preterm pregnancies and early membrane ruptures than in term pregnancies. These data suggest that subtoxic levels of lead could increase the incidence of early membrane rupture and premature deliveries.