The prospect of a "male pill" that would let men enjoy a full sex life with no chance of getting a woman pregnant has moved a step closer.
Scientists in Australia have found a reversible way to stop sperm getting into the ejaculate, without affecting sexual function.
The animal tests showed the sperm could be "kept in storage" during sex.
The findings were published in the journal Proceedings of the National Academy of Sciences.
The quest for the male contraceptive pill has largely focused on getting men to produce non-functional sperm.
But some drugs used for this purpose "have intolerable side-effects," said Dr Sabatino Ventura, one of the researchers at Monash University.
Drugs can induce infertility, but they may also affect sexual appetite or cause permanent alterations to sperm production.