To date, sheep, cattle, and mice have been cloned from adult somatic cells, but scientists at the University of Hawaii School of Medicine (Honolulu, HI) have broken new ground with a type of animal that had not previously been cloned—the male. Earlier somatic cell cloning experiments relied on cells from the female reproductive system, possibly limiting the technique's use for propagating valuable transgenic lines or endangered species. In an effort to overcome this barrier, the University of Hawaii team, whose report appears in Nature Genetics (22, 127–128, 1999), used tail tip cells from male mice as a source of nuclei, which were then implanted into enucleated oocytes. Three of the resulting embryos developed into live male clones of the original donor. The researchers conclude that in principle "precious animals of either sex. . .can be propagated by cloning irrespective of their fertility status." Cloning still has serious limitations—the three surviving clones represent approximately 1% of the embryos transferred, making the current approach too cumbersome for routine use.