The aim of this doctoral thesis was to establish a novel insemination technique in cattle – theendoscopy-mediated intratubal insemination-, followed by a first attempt of practicalapplication. This method allows transferring spermatozoa directly to the site of fertilization viathe infundibulum bypassing most of the female reproductive tract with a minimally invasivetransvaginal approach using endoscopy.In the first part of the study the technique itself has been developed. Sixty-four intratubalinseminations were carried out focussing on semen type (fresh semen, cryopreservedsemen, sex-sorted/cryopreserved semen), semen preparation, semen dose and time ofinsemination. In the second part of the study eight intratubal inseminations were performedon superstimulated heifers using sex-sorted semen. To check whether insemination hassucceeded the oviducts were flushed endoscopically on day 2 post inseminationem andflushing medium was examined for the presence of embryos or unfertilized oocytes.In general, it was shown that endoscopy-mediated intratubal insemination can be appliedsuccessfully independent from semen preparation and semen dose. Despite of using smallexperimental groups, a dose-dependent effect was assessed. In addition, an influence oftime of insemination could be shown. It has to be highlighted that inseminations with very lowsemen doses that contained only one hundredth of that used for conventional inseminationeffectually lead to fertilization and embryo recovery. In the second part of the study,fertilization rates could be elevated from zero to 25 to 30 % after inseminatingsuperstimulated heifers with sex-sorted semen. In future studies, it has to be evaluatedwhether a further shortening of the time between insemination and the expected first ovulations is possible to raise fertilization rates and/or how the life span of spermatozoa canbe extended in the oviduct through the addition of supplements or semen preparationtechniques.In conclusion, this novel insemination technique can be successfully applied. It has beenshown for the first time and repeatedly that oocytes were fertilized in vivo using a semendose of about 0.1 million spermatozoa. Thus, there are potential practical applications incattle breeding in all those cases where only small amounts of semen are available, e.g. theuse of sex-sorted semen or breeding with sires of high genetic merit but reduced semenquality and/or quantity. Besides, intratubal insemination offers a new approach for futureinvestigations on the communication between the oviductal epithelium and spermatozoa aswell as various questions around gametes, fertilization and early embryonic development.