Mice can be cloned from cultured, non-cultured, adult-, fetus-, male-, and female-derived somatic cells at the present day. However, the efficiency of somatic cell cloning is approximately 1–2%, and even in individuals developed to full term, many abnormalities were often shown in cloned mice. Although even the technique itself remains imperfect, embryonic stem (ES) cell lines can be generated from adult somatic cells via nuclear transfer. These cells, which are called ntES cells, exhibit full pluripotency in which they can be differentiated along prescribed pathways in vitro (to produce, for example, dopaminergic neurons) and contribute to the germ line following injection into blastocysts. The rate of establishment of ntES cell lines has been examined for sex and various cell types. This review explains recent advances in mouse cloning to illustrate the strengths and promise of this technique in the study of mammalian biology and biomedicine.