German scientists have announced that stem cells from the testicles of mice may be as useful as embryonic stem cells. "If this turns out to be true, it will be an exciting advance," said George Q. Daley, a leading stem cell researcher at Harvard Medical School. The discovery opens up the possibility that similar cells will be found in adult men.

The key advance in the German research, at Georg August University in Goettingen, was not just isolating spermatogonial stem cells, which generate sperm, but creating a growth medium which coaxes them into becoming cells which can generate any kind of tissue. These cells are called "multipotent adult germline stem cells", or maGSCs. The German team was able to differentiate the maGSCs into beating cardiac and vascular cells, neurons, skin cells and liver cells. More stringent tests remain to be done to confirm the findings.

Critics of the use of stem cells derived from embryos were cautiously optimistic. "This is a big step in the right direction," says Dr Tadeusz Pacholczyk, of the National Catholic Bioethics Center in Philadelphia. "The fact that ethics is being taken seriously in a number of quarters such that alternatives are being explored is a very encouraging development."

The leader of the German team, Dr Gerd Hasenfuss, supports research in both adult and embryonic stem cells. But in Germany, scientists are banned from research on embryos, so he has worked for years to derive multipotent stem cells from adult tissue. This is his first success.