Activity of selenium-dependent glutathione peroxidase and content of selenium in blood were studied during the pregnant women screening. 260 healthy women with pregnancy of 20-34 weeks without any clinical manifestations of hestosis were examined. Decrease of the enzyme activity, correlating with the selenium content, was detected in blood of women with selenium content, was detected in blood of women with clinical forms of hestosis. At the same time, the enzyme activation simultaneously with normal concentration of selenium in blood, were found in some women at the initial steps of toxicosis. Glutathione peroxidase reaction appears to correlate with selenium content during the preclinical steps of hestosis development. Content of selenium in blood of pregnant women as low as 80 pg/ml may be among the risk factors responsible for impairment of the glutathione antioxidation system under conditions of late toxicosis in pregnant women.