Infertile men have been given hope of being able to father their own children in what scientists are calling a major breakthrough.
Researchers have been able to grow sperm outside the body that could mean men don't have to use donor sperm.
The results – reported in the science journal Nature - were created by researchers in Germany and Israel who grew mouse sperm from a few cells in a laboratory dish.
The scientists believe that the same technique - using "germ cells" extracted from the testicles - will eventually work in humans and are now "working as quickly as possible" to that end.
"I believe it will eventually be possible to routinely grow human male sperm to order by extracting tissue containing germ cells from a man's testicle and stimulating sperm production in the laboratory," said Professor Mahmoud Huleihel, who created the Israel results.
Now the scientists who made the discovery have begun experiments that will hopefully lead to the 'Holy Grail' - human sperm grown outside a man's body.
Stephen Gordon, a leading NHS male infertility consultant, praised the breakthrough.
"This is an amazing development that could revolutionise fertility treatment and allow every man to be a natural father," he told the Daily Mail.
Infertile men naturally want to be the father of their child but at present have to accept that can't happen. With the mouse discovery, that could now be a possibility.
The problem of male infertility has grown over the last 50 years and has been matched by huge decrease in sperm counts in men.
"Even with our latest microsurgical techniques there are still thousands of men - who are otherwise healthy -who can't naturally father babies and rely on sperm donation," said Mr Gordon.
Professor Richard Sharpe, one of the UK's top fertility scientists, based at Edinburgh University, who hopes to work on the project, said: "This is a significant step forward towards making human sperm.
"We have already applied the same tests as we did with mice in the laboratory, using human cells, but as yet have not had success. We are confident that if it can be done in a mammal such as a mouse it can be done in humans.
"We are experimenting with a number of different compounds to get the germ cells to grow into sperm. And we believe it will be possible. And, hopefully, soon."