US scientists have developed two new ways of generating embryonic stem cells, designed to avoid some of the ethical objections to current methods that involve destroying "potential human life". The journal Nature published papers on both techniques in its online edition yesterday. They work well in mice and the researchers believe they could be applied to human stem cells. The more positive technique comes from Advanced Cell Technology (ACT), a Massachusetts biotechnology company, working with scientists at the University of Wisconsin. In a procedure similar to that used in pre-implantation diagnosis to test human IVF embryos for genetic defects, they removed a single cell from a newly fertilised mouse embryo and grew embryonic stem cells from it.