Sperm may smell their way to the egg, which researchers say could lead to advances in contraception and fertility treatments.
Sperm cells are attracted towards the egg
German researchers trying to work out how sperm find their way to their intended destination have identified an odour receptor in testicular tissue, usually found in the sensory nerve cells of the nose.
In laboratory tests, the receptor kick-started a process where sperm were drawn towards concentrations of an artificial scent called bourgeonal, which triggers the receptor in nasal cells.
The next stage of the research is to find the sperm-attracting substance produced by the female reproductive system.
It's not just about sperm swimming around until they find an egg
Dr Allan Pacey, Sheffield University
The same process has been seen in sea urchins, where sperm cells seek out sperm-attracting substances produced by sea urchin eggs.
If successful, this could help fertility doctors identify the most mobile sperm, increasing the chances of successful treatment.
Dr Marc Spehr of the Ruhr-Universitšt, Bochum, who led the research, said: "If a natural equivalent to bourgeonal is, at least in part, responsible for successful pathfinding or screening of fertile sperm, then it should be possible to use bourgeonal within IVF treatments."
"Some of the difficulties experienced in IVF treatments may be linked to the 'quality' of sperm.
"Bourgeonal might be used in the future to find the motile and fast sperm cells that are needed for fertilization."
A substance called "undecanal" which appears to block the affect of bourgeonal was also identified.
Dr Spehr said undecanal could be used to design new contraceptives.
He said: "One of the greatest problems in contraception these days is the use of hormones.
"If undecanal can inhibit egg-sperm communication, this drug might be used, after a great deal of future research, to prevent undesired pregnancies.
"One could speculate about delivery of undecanal into the female genital tract or even about drugs containing equivalents to undecanal that could be used by men."
Odorant receptors have been identified on sperm before, but this study shows they seem to be involved in regulating sperm's behaviour.
Researchers cloned the receptor and used human embryonic kidney cells to look at how it behaved.
When the receptor moved towards concentrations of the sperm attractant, it sets of a similar physiological process as it does when it triggers when a smell is being detected by the nose.
Dr Allan Pacey, senior lecturer in andrology at Sheffield University, told BBC News Online: "This study is potentially very exciting as scientists have been searching to demonstrate whether or not sperm really are attracted to the egg in mammals.
"What it illustrates is that the process of sperm transport to the egg is not just about sperm swimming around until they find an egg.
"It is likely to be highly coordinated and involving a number of different mechanisms of which odorant receptors may play an important role.
"They have added another piece to the jigsaw. But it's a big puzzle.
"What has yet to be shown is what sperm are actually attracted to, if anything, but this should now be possible using the techniques described in this paper."
He said it may be possible to screen for the absence or presence of the receptor as a diagnostic test to explain why some men are have more difficulty than others in conceiving with their partner.
The research is published in the magazine Science.