American researchers say they have isolated stem cells in human ovaries that spontaneously produced new eggs in the laboratory.
The scientists say it may be possible eventually to create an unlimited supply of human eggs to help fertility treatment.
A long-held theory is that women are born with all the eggs they will ever have. But researchers say they have shattered that idea by finding the stem cells which produce new eggs, the BBC reports.
Doctors at Massachusetts General Hospital used unique proteins on the surface of stem cells to fish them out of ovarian tissue.
The study published in Nature Medicine showed that growing these cells in the laboratory resulted in new eggs being produced spontaneously.
There are tight legal and ethical restrictions on research on human eggs. The same experiments repeated using stem cells taken from mice showed the eggs could be fertilised with sperm and produced embryos.