NUCLEAR transfer has been used in mammals as both a valuable tool in embryological studies1 and as a method for the multiplication of 'elite' embryos2–4. Offspring have only been reported when early embryos, or embryo-derived cells during primary culture, were used as nuclear donors5,6. Here we provide the first report, to our knowledge, of live mammalian offspring following nuclear transfer from an established cell line. Lambs were born after cells derived from sheep embryos, which had been cultured for 6 to 13 passages, were induced to quiesce by serum starvation before transfer of their nuclei into enucleated oocytes. Induction of quiescence in the donor cells may modify the donor chromatin structure to help nuclear reprogramming and allow development. This approach will provide the same powerful opportunities for analysis and modification of gene function in livestock species that are available in the mouse through the use of embryonic stem cells7.