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Since the report of “Dolly”, the cloned sheep, great progress has been made in the improvement of cloning technology and viable offspring have been cloned in several mammalian species, including sheep, cattle, pig, goat, horse, mule, cat, mouse, rabbit, rat, dog, wolf, ferret, buffalo, camel. Somatic cell nuclear transfer involves five major steps, i.e. enucleation of the recipient oocyte, transfer of the donor cell, fusion, activation and culture of the reconstructed embryo. Cloning technology is still characterized by relatively low success rates and a certain proportion of the offspring shows abnormalities (specifically ruminants, mice) known as the “Large Offspring-Syndrome” (LOS). In cattle, success rates are higher (15-25% live offspring based on the number of transferred embryos) and viable offspring can be produced from cloned embryos on a regular scale. Due to important modifications of the cloning protocol, we can now routinely produce cloned transgenic pigs with high levels of efficiency. Transfer of nuclear transfer complexes into oviducts of recipient animals prior to ovulation significantly improved success rates of porcine cloning. Fourteen pre-ovulatory transfers resulted in 11 pregnancies with a total of 56 cloned transgenic piglets born. All offspring had normal birth weights (1.0-1.5 kg) and showed no malformations. Average litter size was 5.2; the overall efficiency was 3.1% and 4.4% when related to pregnant recipients.