The production of monozygotic twins/multiplets in livestock animal can be achieved either by microsurgical bisection of embryos at the morular- or blastocyst stage, isolation and proliferation of blastomeres from early cleavage stages or nuclear transfer. While the success rates of micro-surgical bisection are high in ruminants (pregnancy rates approximately 50%, twinning rates 20-40%) in polyovulatory species such as swine, the efficiency is low with an average of 20% embryonic survival and 2% monozygotic twins that can positively identified via DNA-fingerprinting. Isolated blastomeres from multicellular embryos still possess great developmental capacity in vitro to progress to the blastocyst stage. However, their development in vivo is markedly reduced. This article summarizes the results obtained by the authors during several years of investigation. The results show for the first time that identical twins can be obtained in pigs which have been demonstrated to be a useful tool in biomedical research.