Interest in mechanisms of embryo implantation is increasing, particularly with the realization that failure of implantation after in vitro fertilization and embryo transfer places significant limits on the success of treatment. In addition, there is a need to provide hypotheses, and ultimately mechanisms, for the high rates of embryonic loss in women in the population at large. Traditionally, implantation research has concentrated on genetics and endocrinology without providing many therapeutic benefits. A new era is now beginning with the application of modem cellular and molecular approaches to the investigation of the relationship between trophoblast and endometrium. At the same time, older data can be reevaluated in the light of current research into cell cell and cell-matrix interactions. The feeling that new avenues of research are open was apparent when an international group of scientists came together at a workshop on "The Cell Biology of Trophoblast Invasion In Vivo and In Vitro" held during the XXIV Annual Meeting of the Cell, Tissue and Organ Culture Study Group (C.T.O.C.) at Heidelberg in 1986. What was unusual about this Conference was the interdisciplinary dialogue between implantation researchers and tumor biologists, highlighting aspects common to invasion of trophoblast and tumor cells."

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 evidence that the efficacy of these contraceptives lies with other factors as well, for example their influence on sperm migration and capacitation or their influence on the transportation of the unfertilized egg. On the other hand there appears to be more im portance in their influence on the blastocyst and on the early stages of implantation (Carol et aI., 1973; Duncan and Wheeler, 1975; Hafez and Evans, 1973; Oettel, 1975). These stages in development are characterized by complex interactions between em bryo and mother, which have only lately been more exhaustively investigated and which are still subjects of intense research (Beier, 1973, 1974a; Blandau, 1971a; Finn and Porter, 1975; Hafez and Evans, 1973; Steven, 1975). It is expected that insight in to the mechanism of the action of postcoital contraceptives and a possible basis for the development of new concepts in contraception can be gained here."