A method is described for the production of an animal (offspring) by the process of nuclear transfer. The animal may be produced using donor genetic material in cells taken directly from any stage of an animal, such as an embryo, foetus or adult or from cell cultures established from material from any stage of an animal, such as embryonic, foetal or adult material. The process may be used to introduce genetic modifications into the resultant offspring by genetic manipulation and selection of the cells to act as nuclear donors prior to embryo reconstruction.The present invention provides a method of reconstituting an animal embryo, the process comprising transferring a nucleus into a first oocyte followed by removing and transferring the nucleus from the oocyte to a further oocyte or to an enucleated fertilized zygote.