OBJECTIVE To explore the effect of deficiency of blood selenium and placental selenium on the damage of histomorphology of the placentas in ICP. METHODS We measured the selenium concentration by a catalytic polorographic method in blood and placenta and glutathione peroxidase (GSH-Px) activity by a 5,5'-dithionbis (2-nitrobenzoic acid) direct method in blood in 30 women with ICP (ICP group) and 30 normal pregnant women (control group). Furthermore, the features of the placentas (10 from control group and 10 from ICP group) pathologic changes were observed microscopically. RESULTS (1) The selenium concentrations in blood (0.0389 +/- 0.0090) mg/L and placenta (0.3770 +/- 0.0964) mg/kg and the activity of GSH-Px (59.31 +/- 11.42) U in ICP group were found to be significantly lower than those in blood (0.0477 +/- 0.0094) mg/L and placenta (0.4554 +/- 0.0626) mg/kg and the activity of GSH-Px (68.48 +/- 10.47) U in control group, respectively (P < 0.002). (2) The activity of GSH-Px had a significant positive correlation with selenium concentration in blood in ICP group (r = 0.05498, P < 0.001) and in control group (r = 0.06234, P < 0.001). There was a positive correlation between blood and placental selenium concentrations in ICP group (r = 0.6473, P < 0.001). On the other hand, there was not correlation in women with normal pregnancies. (3) Placentas obtained from women with ICP had swelling and fibrinoid necrosis of villi, increasing number of syncytial sprouts, thickening of vasculo-syncytial membrane (VSM) and decreasing size of the intervillous space under light microscopy. Placentas from control group did not show the pathologic changes as mentioned above. CONCLUSIONS As selenium constitutes the active part of GSH-Px, these results suggest that the placental selenium deficiency may lead to reduced placental GSH-Px activity and the antioxidative defence may have been defective which may be associated with the damage of histomorphology of the placentas in ICP.