Scientists believe the human testicle may provide a less controversial source of cells for stem cell research.
Stem cells hold the promise of many new treatments
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 describes in the journal Nature how it isolated cells from mice testes that seem equally useful.
The researchers believe similar cells could also be extracted from humans.
Scientists already knew certain cells in the testes of newborn mice were able, like embryonic stem cells, to generate numerous different tissue types.
But until now they had not been able to show the same cells existed in adults.
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.
They called these cells multipotent adult germline stem cells (maGSCs).
Like ES cells, maGSCs can spontaneously differentiate into the three basic tissue layers of the embryo - and contribute to the development of multiple organs when injected into embryos.
Professor Chris Higgins, director of the Medical Research Council's Clinical Sciences Centre, said: "The possibility of using cells from the testes as an alternative to embryonic stem cells for therapy is intriguing.
"However, much more research is required before the similarities and differences between these testes cells and embryonic stem cells are understood, and before their potential for use in therapy can be properly assessed."
Professor Harry Moore, of the Centre for Stem Cell Biology at the University of Sheffield, UK, said there were a number of key differences between mice and human testes cells.
Mice cells proliferated readily, but the same was not true for human cells. There was also a significant difference in the chemicals that each employed to grow.
However, he added: "Nevertheless, the paper offers an intriguing route for future stem cell therapy which might overcome the use of embryos and cloning."
A Department of Health spokesperson said: "The government is investing £100m in stem cell research over the next two years.
"This includes research on all types of stem cells - embryonic, umbilical and adult.
"It is important we look into all types of stem cells to make sure no opportunities for new treatments are missed."