A method of reconstituting an animal embryo involves transferring the nucleus from a quiescent donor cell into a suitable recipient cell. The donor cell is quiescent, in that it is caused to exit from the growth and division cycle at G1 and to arrest in the G0 state. Nuclear transfer may take place by cell fusion. The reconstituted embryo may then give rise to one or more animals. The invention is useful in, the production of transgenic animals as well as non-transgenics of high genetic merit.