Maternal and cord blood samples were collected in 60 cases with or without rupture of membranes before and at term. Serum concentrations of calcium, copper, iron and zinc were determined by proton-induced X-ray emission. Maternal and cord serum cerulo-plasmin and maternal hemoglobin were also determined. Mothers with preterm delivery showed significantly lower hemoglobin values than those with delivery at term. Concentrations of calcium, iron and zinc were higher in cord than in maternal serum whereas maternal copper levels were higher than respective cord levels in all groups. The cord copper and ceruloplasmin and also their fetal/maternal ratios were significantly lower in the group with preterm premature rupture of fetal membranes (PROM) than in other groups. Maternal serum zinc and calcium were lower in preterm groups than in term groups. The study suggests a possible role of copper in preterm PROM and of zinc in the initiation of preterm labor, whereas calcium and iron do not seem to be involved in the etiology of prematurity or PROM.