The Se concentration in maternal and cord whole blood and plasma was determined spectrofluorimetrically in: (1) 42 women at term and (2) 46 at preterm parturients, and in the placenta. The glutathione peroxidase (GSH-Px) activity was measured in red cells and plasma in maternal and cord blood of both groups. The Se concentrations and GSH-Px activities of the above-mentioned groups were compared with those of non-pregnant women. Whole blood and plasma Se concentration of parturients at term did not differ significantly from those of non-pregnant women (72.3 versus 80.3 ng ml-1 whole blood and 48.7 versus 56.2 ng ml-1 plasma). In preterm parturients, however, Se concentrations were significantly lower (61.1 ng ml-1 whole blood and 39.2 ng ml-1 plasma) when compared with term parturients. The Se levels in cord blood and plasma were similar to their mothers' Se concentrations. No difference was observed in placenta Se levels (130 ng g-1 wet weight in both groups). The same was true for glutathione (GSH): the concentration in maternal and cord blood of term and preterm parturients did not differ and varied from 2.43 to 2.50 mmol l-1 red cells. Red cell GSH-Px activities were similar in maternal and cord blood of both term and preterm groups and ranged from 14.3 to 15.7 U g-1 Hb. The plasma enzyme activity in the maternal blood of preterm parturients was significantly (p < 0.05) lower than that of mothers at term delivery. The GSH-Px activity in the plasma of cord blood was significantly (p < 0.001) lower in the preterm than in the term group. It is suggested that low Se levels in the blood of women at preterm delivery, as shown here, may be one of the causes of retinopathy and respiratory distress syndrome in preterm infants.