Objective. to study the morphological and immunohistochemical changes in the placenta and the area of the placental site in patients with preeclampsia, including in those who died from its severe forms and complications. Subjects and methods. The investigators studied morphological and immunohistochemical changes in the components of afterbirth in 16 puerperas with preeclampsia and in 7 healthy puerperas, as well as those in placental and uteroplacental tissue in 8 patients who had died from severe preeclampsia/eclampsia. A comparison group included 3 patients who had died from other causes (without preeclampsia). An immunohistochemical examination was aimed at visualizing neuron-specific enolase (NSE) in the tissues, by using -NSE mouse monoclonal antibodies. Results. Complete gestational rearrangement of the endometrial and myometrial segments of uterine spiral arteries, moderate NSE immunoexpression in the invading cytotrophoblast cells, and as well as the NSE-negative epithelium of placental villi were stated in all the patients from the comparison group. All the patients who had died from severe preeclampsia and eclampsia were found to have a final stage of inadequate cytotrophoblast invasion with a clear NSE immunovisualization in the invading cytotrophblast cells. In preeclampsia, the epithelium of the placental villi was also NSE-negative. The immunohistochemical examination of placental components in the preeclamptic puerperas discharged from hospital supported the data obtained from the analysis of autopsy specimens. Conclusion. Detection of NSE in the invading cytotrophoblast cells is indicative of the potentially antigenic nature of the forming placenta; impairment of this process may give rise to an immune conflict between the mother and her fetus, including to the development of preeclampsia.