A team of scientists has reported producing viable sperm using the stem cells of mice in an experiment that researchers hope could one day lead to treating infertile men.

The Kyoto University researchers managed to induce mice stem cells into creating sperm precursors, which were transplanted into infertile male mice. The mice then produced sperm that was successfully used to fertilize eggs in a lab dish.

The offspring were healthy and fertile, according to a paper published online in the scientific journal Cell.

Members of the research team, led by Mitinori Saitou, say they believe their success may help in the development of infertility treatments in humans, although they say many hurdles remain.

"We have high hopes, but it's not that easy," Saitou says. "There are many difficult issues ahead in applying this to humans. But it is a first step."

Experts outside the group say it's an important first step toward infertility treatment.

"This is a very good experiment for thinking about treatment of infertile man but a very very long way," says Toshio Suda, developmental biology professor at Keio University.