[Capabilities and limitations of research].

Assisted human reproduction (AHR) currently solves numerous difficulties caused by sterility in couples. However, it poses some problems whose solutions involve three main directions in research. Fundamental research explores spontaneously occuring phenomena. It shows that over and above common general points of sexual reproduction, mechanisms can differ from one to another. Technical research perfects artificial empirical methods which lead to fertilization, implantation and pregnancy. It shows that success varies from one species to another. Concerning some technologies such as intracytoplasmic sperm injection, successful results began with humans where they seem to be easier to obtain. Research of risks cheks, in animals, the absence of adverse effects of the above techniques for conceptus. It has confirmed the harmfulness of some environmental factors for gametes and zygotes. Moreover, it shows that these negative effects vary between species and within them for strains and sex. For instance, the cryopreservation of mouse embryos leads to changes in the offspring concerning morphophysiological and behavioral features, some of them appearing in elderly subjects. Indeed, these changes vary as a function of strain and sex. These results as a whole show that experimentation on animals can indicate research areas and also give rise to the need for caution. However, if we want to act on human reproduction, they also show, because of the variations in reactivity from one species to another, that the animal model is insufficient and that research in man is essential. From this point of view, a long term follow up of AHR children seems necessary, as well as the need for reflexion concerning the possibility and conditions of research on human embryos.