From BBC News:
Stem cells hold great promise for new treatments for many conditions as they have the ability to become many different types of adult tissue. But at present the most flexible type is found in human embryos – and their use is mired in controversy. A German team describe in the journal Nature how they isolated cells from mice testes that seem equally useful. The researchers, from the Georg August University in Gottingen, isolated sperm-producing cells from the testes of adult mice. They were able to show that, under certain culture conditions, some of them grew into colonies much like embryonic stem cells.
More here.