Say you're a woman who wants to have fertility treatment but can't afford the $5,000 to $6,000 cost.

What if you could get it for half-price, by agreeing to donate half the eggs you produce for stem cell research?

Interested?

British women may get a crack at that deal in a few months, under a plan pursued by Dr. Alison Murdoch of Newcastle University.

This concept, which resembles a strategy sometimes used to get eggs for fertility treatment, is just one of several new efforts to boost the supply of human eggs needed for research. The shortage has triggered an ethical debate on both sides of the Atlantic: Should women be paid for supplying eggs?

Scientists need eggs for a process called therapeutic cloning, which creates stem cells genetically matched to an individual. It may be used someday to create tissue to treat illnesses like diabetes and Parkinson's disease, providing transplant material that's genetically matched to the patient so that it won't be rejected. Therapeutic cloning may also help scientists develop better drug treatments.

The process involves transferring DNA into human eggs and growing them into 5-day-old embryos, from which stem cells are harvested.

It's not clear just how many eggs scientists need for this research. But it is clear that for a woman, donating eggs is a significant undertaking.

By various estimates, a woman can spend 40 to 56 hours in medical offices, being interviewed, counseled and subjected to a surgical procedure, under sedation, that retrieves eggs from her body. Before that procedure, she takes hormone injections daily for more than a week to stimulate egg development.

Women donate thousands of eggs in the United States every year to help other women have babies. They are paid. The American Society of Reproductive Medicine doesn't recommend a figure but says $5,000 or more requires some justification and that $10,000 is too much. (In fact, some ads for eggs offer far more).

The medical group also says it's fine to pay women for producing eggs for stem cell research. But other guidelines and laws on that topic favor just reimbursing women for expenses. That's the word from the law books of California and Massachusetts and a committee of the National Research Council, a congressionally chartered nonprofit organization that advises the federal government.

In fact, the compensation question has split American feminists and advocates for reproductive health and rights, said Marcy Darnovsky, associate executive director of the Center for Genetics and Society. One side says offering money beyond reimbursement risks exploiting disadvantaged women by offering undue inducement to participate, while the other side calls that stance paternalistic, she said.

Darnovsky said her center has no position on paying women to provide eggs for fertility clinics, but holds that if women give eggs for stem cell research, they should only be reimbursed for expenses, including lost wages.

Why the difference? It's a matter of a woman's gauging the risks and benefits of donating her eggs, Darnovsky said.

On the risk side, there's been too little follow-up of women to know for sure how safe the egg-retrieval process is, she said.

On the benefit side, while donating eggs to a fertility clinic often produces a baby, the potential payoff in stem cell research is promising but only speculative at the moment, Darnovsky said. But women, like society, have so bought into the expectation of "miracle cures" from stem cells that they overestimate the benefit from donating eggs, she said.

The result? If stem cell researchers offer the kind of money that fertility clinics do, "I think any woman who's trying to pay the rent and put food on the table, and people who don't have a lot of money to spare, are going to be tempted to discount the risks and overvalue the benefits," she said.

Similarly, ethicist Laurie Zoloth of Northwestern University believes that paying compensation could exploit some women. Women who give eggs to fertility clinics are doing it for the money, she said, and as a society, "we don't ... want the bodies of the poor used for the needs of the wealthy."

"You do not see many full professors or CEOs selling eggs to secretaries or housecleaners," she said in an e-mail.

Zoloth, who emphasized that she strongly supports stem cell research that would use the eggs, said she believes women donating eggs for such research should only be reimbursed for expenses. Giving up eggs, like donating organs, should be an altruistic act, she said.

But others believe women should be paid.

Participants in other kinds of biomedical research are compensated for their time, inconvenience and rigors of participating, says Kathy Hudson, director of the Genetics and Public Policy Center at Johns Hopkins University. So why, she asks, should egg donors be treated any differently?

There are ways to guard against exploitation of vulnerable women, she said. One would be for local boards that oversee research to make sure that donors are recruited from a wide variety of groups rather than just the economically disadvantaged, she said. And limits can be set on the number of times any one woman can participate, she said.

So far, the track record for altruistic donations is mixed. On one hand, hundreds of women volunteered to donate eggs in South Korea for research by the now-disgraced scientist Hwang Woo-suk, who fraudulently claimed success in therapeutic cloning.

But Dr. Robert Lanza, vice president of research and scientific development at Advanced Cell Technology Inc. of Alameda, Calif., said he has given up trying to get donations without compensation. After more than a year of pursuing that strategy and about 100 advertisements, ACT was able to get only one woman to donate eggs, he said in an e-mail.

And Kevin Eggan of the Harvard Stem Cell Institute, who's been seeking eggs since May in return for reimbursing out-of-pocket expenses, said recently that the effort had generated some calls but no donors yet. The approach must be given more time to work, he said.

Murdoch, who also directs a fertility treatment center in Newcastle upon Tyne, said that when her lab asked fertility-clinic patients to donate eggs, it received only 66 over seven months. That's just not enough, she said.

In contrast, if her new plan attracts two women a week -- chosen because they appear likely to produce lots of eggs -- it would provide 20 eggs each week. That's still not a lot, but the supply should be steady, she said.

Her "egg-sharing" plan resembles an arrangement that's used occasionally at fertility clinics. In that plan, a woman shares her eggs and treatment costs with another woman who wants a baby.

Murdoch's group has permission from Britain's Human Fertilization and Embryology Authority to set up the arrangement for stem cell research. Now it's a question of raising money to finance it. Murdoch said she hopes to start offering the deal to British women in a few months, and that she has already heard from dozens of women eager to participate.

Though the HFEA approved Murdoch's plans in July, it has since started gathering public and expert opinions on whether egg sharing should be permitted. "If the consensus is that this is not a good idea, we can change the policy, and rescind the license," said John Paul Maytum, an HFEA spokesman.

The idea has drawn some opposition.

"I think it smacks of offering financial inducement to women to donate eggs specifically for research," said Dr. Stephen Minger, director of the stem cell biology laboratory at King's College in London. "You will be exploiting women for money," said Minger, who says that participants would be convinced to undergo the treatments for financial gain.

Hudson agreed, saying it would appeal to women of limited means who are "desperately trying to get pregnant" and offers the possibility of a baby in return for eggs. "How is that not undue influence?" she asked. "How can that possibly be OK, and it's not OK to compensate a normal, healthy volunteer?"

Murdoch says that as long as women provide informed consent, she believes that egg-sharing is no different from standard medical practices, such as giving blood or participating in drug trials.

"It almost becomes a feminist issue," said Murdoch. "I would take exception to the fact that society feels that women need to be protected from themselves."

Some stem cell scientists are skirting the debate by finding other sources of eggs. Dr. George Daley of Harvard's stem cell institute announced in June that he would use eggs originally produced for fertility treatment but which failed to become fertilized. Usually, such eggs are discarded, but women in the fertility program Daley works with must agree to their use in research.

Renee Reijo Pera of the University of California, San Francisco, is also working with eggs originally produced for a fertility clinic, but which turn out to be immature. Such eggs are not routinely used in clinics, though they can be matured in a lab.

Reijo Pera noted such lab-matured eggs can produce babies, so "the egg is not going to be the problem" in her stem cell work, she said.

Lanza said ACT is also working with fertility clinics to get immature eggs.

In any case, the need for eggs may only be temporary.

They are, in fact, only a tool to reprogram the inserted DNA so that it will drive the development of an early embryo. Scientists hope to learn enough about that reprogramming process to let them take an ordinary cell from a person and use it to produce other kinds of cells, perhaps without going through an embryo stage. That might happen in 10 years, Murdoch estimated.

And then they wouldn't need eggs any more.