Binucleate trophoblast giant cells are a characteristic feature of the ruminant placenta. During pregnancy, these fetal cells are continuously produced and fuse with maternal uterine epithelial cells. One purpose of this process is the release of several mediator substances into the maternal organism, by which the fetus can influence the maternal metabolism. Using immunohistochemical und electronmicroscopical techniques we investigate the generation, maturation and decline of the binucleate trophoblast giant cells in the bovine placenta. The information will give better insight into the pathogenesis of the retention of fetal membranes, which is a common problem in bovine reproduction.