A contraceptive pill for men has moved a step closer to becoming reality after researchers unlocked a safe and reversible way to make it work.
The key to the 'holy grail' for fertility scientists lies in a pair of proteins that stop sperm cells launching during ejaculation, they say.
Mice which had been genetically modified to suppress the proteins were found to be completely infertile but had a normal sex drive.
There were no side-effects and they were able to father offspring by artificial insemination.
"This bypasses perhaps the greatest stumbling block in the quest for a socially acceptable male contraceptive," the Australian and British researchers wrote in the journal PNAS.
They say drugs that block one of the proteins already exist and trials may start once a drug to block the other is identified.