Term placental villous fragments from normotensive pregnant women were incubated under hypoxia in order to induce lipid peroxidation of the placental plasma membranes and, consequently, to increase their release of lipid peroxide products into the incubation medium. The homogenates of the villous fragments were assayed for plasma membrane Ca-ATPase (PMCA) activity and TBARS. The incubation medium, after placental hypoxia, was used to incubate intact red blood cells (RBCs) from normotensive pregnant women. Similarly, intact RBCs from normotensive pregnant women were incubated with deproteinized blood plasma from normotensive pregnant women and women with preeclampsia. In all the cases, red cell ghosts were prepared from the incubated cells and assayed for PMCA and TBARS. The incubation of placental villous fragments under hypoxia led to an increase in the TBARS and a significant reduction in the PMCA activity of their homogenates, as compared to those of villous fragments incubated under normoxia. The exposure of intact RBCs from normotensive pregnant women either to the incubation medium of placental hypoxia or to deproteinized blood plasma from women with preeclampsia, caused a rise of the TBARS and a diminution of PMCA activity of the red cell ghosts. Inside-out vesicles were also prepared from intact RBCs incubated with the medium where the placental hypoxia was carried out. These vesicles were assayed for active calcium transport. Pretreatment of RBCs with the incubation medium of placental hypoxia led to a lower active calcium transport as compared to that of inside-out vesicles from RBCs without any preincubation. These results are in agreement with the idea that the RBCs can be peroxidized when passing through a highly oxidized medium, such as the placental intervillous space from women with preeclampsia. The peroxidized RBCs would contribute then to the propagation of lipid peroxidation from the placenta to nearby and far away tissues.