Women not undergoing fertility treatment can donate their eggs to medical research, the UK's fertility regulator has announced.
Eggs can be used in stem cell research
The Human Fertilisation and Embryology Authority said women would not be paid for "altruistic donation" but would be eligible for expenses.
Some scientists say they need human eggs for the creation of embryos from which stem cells can be derived.
But critics say egg donation involves potential health risks.
Previously women have only been able to donate spare eggs produced through IVF or gynaecological treatment, such as sterilisation.
Now women choosing to donate their eggs to researchers will be able to claim up to £250 in expenses.
The HFEA also said women should be allowed to donate through "egg-sharing" schemes, in which they receive cut-price IVF in return for handing over eggs.
Angela McNab, chief executive of the HFEA, said: "The Authority has decided that women will be allowed to donate their eggs to research, both as an altruistic donor or in conjunction with their own IVF treatment.
"Given that the medical risks for donating for research are no higher than for treatment, we have concluded that it is not for us to remove a woman's choice of how her donated eggs should be used."
Earlier this year, the team at the Centre for Life in Newcastle was awarded a temporary licence to offer discounted IVF treatment if patients donate eggs for research.
The centre was also given the UK's first licence to begin recruiting women donors who are not already having medical treatment.
Professor Alison Murdoch, who is director of the Newcastle Fertility Centre at Life, said: "Women are capable of making their own minds up about whether or not they donate their eggs for research. Society should respect their autonomy."
Professor Peter Braude, director of the Centre for Preimplantation Genetic Diagnosis at Guy's and St Thomas' Foundation Trust, said: "Women have been donating eggs for more than 20 years, usually those undergoing sterilisation where the eggs would be used to study early embryonic development.
"The difference now is that women are being asked as volunteers where their ovaries would be stimulated to develop eggs specifically and solely for research."
He added: "I do not see a problem with that."
But some experts were unhappy with the ruling.
Dr Stephen Minger, an expert in stem cell research at King's College London, said work using human eggs was still in its infancy, and it was premature to be encouraging women to hand over their eggs for research.
He said the method used to retrieve eggs required the use of powerful hormones, and the insertion of a needle through the wall of the uterus.
"Many of us have said lets perfect this technology using alternative sources of eggs, such as cow eggs, until it does become justified to look for altruistic donation of eggs for these procedures.
"I think it is just to early for us to be encouraging this to happen."
Josephine Quintavalle, director of the campaign group Comment on Reproductive Ethics, said: "Risks associated with egg harvesting are widely acknowledged, particularly in response to ovarian hyperstimulation."
Anna Smajdor, researcher in Medical Ethics at Imperial College, said women should be offered fair payment for donation.
"The advantage is all on the side of those who already stand to gain, while altruistic donors assume all the risks and receive none of the benefits."
Fertility expert, Lord Robert Winston, said paying women to donate eggs for research already happens for other tissues, for example in patients giving samples as part of drug trials.
However, he added women being offered free IVF treatment in return for donating their eggs to other women with fertility problems was concerning.
"Women have been paying for eggs in Britain for a very long time, because there is egg sharing, a trade in eggs, which is really quite worrying and the HFEA have sanctioned that."