The establishment of the morphologically and physiologically intimate contact be- tween two genetically different individuals, mother and embryo, which takes place during implantation, has always exerted a fascination on researchers in biology and medicine. Recent years have also seen the beginnings of a more practice-oriented med- ical interest in this event, as certain methods of contraception whose use is ever in- creasing, namely intra-uterine devices (IUDs) and post-coital oral contraceptives, are based on it. On one hand, we have fairly well substantiated experimental and clinical...