Abstract. The aim of the present study was to clarify the overall efficiency of porcine somatic cell nuclear transfer (SCNT) by incorporating cryopreservation of the cloned embryos before transfer. The SCNT embryos reconstructed with preadipocytes and in vitro-matured (IVM) oocytes were cultured to harvest morula stage embryos; they were then subjected to delipation (removal of cytoplasmic lipid droplets) and vitrification. After warming and culture, the embryos developing to blastocysts were transferred to recipients to obtain cloned piglets. From 372 reconstructed embryos, 188 (50.5%) reached the morula stage and 117 (31.5%) developed to blastocysts after vitrification. Transfer of 98 (26.3%) morphologically normal blastocysts gave rise to 6 (1.6%) piglets, including 1 stillborn. The efficiency of the cloned piglet production was comparable with that obtained using SCNT embryos without cryopreservation (2.7%, 17/ 635). Here, we demonstrate that porcine somatic cell cloning can be performed without a significant reduction in efficiency even when the SCNT embryos are cryopreserved before transfer. Key words: Pig cloning, Somatic cell nuclear transfer, Vitrification (J. Reprod. Dev. 57: [312][313][314][315][316] 2011) n recent years, pigs have often been used as large laboratory animals in biomedical research [1][2][3][4][5][6][7], and genetically engineered pigs are highly desired in rapidly advancing research areas, such as regenerative medicine, organ transplantation, analysis of intractable genetic disorders and stem cell therapy [for review, see 7]. For the production of genetically engineered pigs, including gene knockout pigs, somatic cell cloning is a key technology [8][9][10][11][12][13][14][15]. Therefore, if a reliable cryopreservation technique for cloned embryos can be established, the production and application of various specially designed pigs will advance further.We conducted the present study to elucidate the conditions that could achieve a high survival rate of cloned porcine embryos after cryopreservation in a stable manner. We previously showed that, for the cryopreservation of porcine IVM-derived embryos, it is effective to combine vitrification and delipation, a process for reducing the amount of lipid droplets in the embryonic cytoplasm [16,17]. We have also confirmed in our previous studies that delipation of porcine in vitro-produced embryos at the morula stage is less injurious than when done at the early cleavage stages or the blastocyst stage [16][17][18][19]. In addition, it was shown that vitrification of delipated porcine embryos at the morula stage results in a high postwarming survival rate [16,18,19]. In conjunction with these studies, we carried out a study of the vitrification of porcine cloned embryos at the morula stage. The overall efficiency of cloned pig production by SCNT with cryopreservation (i.e., how many cloned piglets could be produced from all of the SCNT embryos prepared via cryopreservation) was clarified.In the cryopreservation experiment, the SCNT embryos ...