Several mammals — including sheep, mice, cows, goats, pigs, rabbits, cats¹, a mule², a horse³ and a litter of three rats⁴ — have been cloned by transfer of a nucleus from a somatic cell into an egg cell (oocyte) that has had its nucleus removed. This technology has not so far been successful in dogs because of the difficulty of maturing canine oocytes in vitro. Here we describe the cloning of two Afghan hounds by nuclear transfer from adult skin cells into oocytes that had matured in vivo. Together with detailed sequence information generated by the canine-genome project^{5, 6}, the ability to clone dogs by somatic-cell nuclear transfer should help to determine genetic and environmental contributions to the diverse biological and behavioural traits associated with the many different canine breeds^{7, 8}.

1. Department of Theriogenology and Biotechnology, College of Veterinary Medicine, Seoul National University, Gwanak-gu, Seoul 151-742, South Korea
2. Pittsburgh Development Center, Magee-Womens Research Institute, Departments of Obstetrics–Gynecology–Reproductive Sciences and Cell Biology–Physiology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15213, USA

Correspondence to: Woo Suk Hwang¹ Email: hwangws@snu.ac.kr

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