Lipid peroxides, glutathione, and metals (lead, cadmium, and arsenic) were measured in pregnant women residing in the vicinity of a copper smelter. A diagnosis of pregnancy complications experienced by each woman was made on the basis of interview and clinical record. Patients were assigned to groups of normal or pathologic pregnancies (threatened spontaneous abortion, toxemia, and anemia) according to this diagnosis. Biochemical changes suggestive of increased lipid peroxidation and decreased antioxidant protection (involving the reduced: oxidized glutathione balance) were found in the diagnostic groups of pregnancy complications. These changes were independent of measured maternal variables. Maternal exposure to metals (as indicated by blood lead and cadmium) was associated with a decrease in reduced glutathione in blood. Since increased lipid peroxidation has been implicated in other studies as a pathogenetic factor for maternal toxemia, it is suggested that exposure to metals during gestation could enhance the development of pregnancy complications by increasing lipid peroxidation via depletion of reduced glutathione reserves.