Robert Lanza, vice president of research at ACT, says the company has already had problems securing egg donors. "We ran an exhaustive recruitment program over the last six months, with disappointing results," he says. While more than 100 women replied to advertisements for egg donors, according to Lanza, almost all of them dropped out of the process when they learned about the time and medical procedures involved. Lanza says they now have one donor who has signed consent forms for egg donation.

Worries over egg donation are not new -- concerns have cropped up repeatedly as a handful of groups have attempted human nuclear transfer research in the last few years. Most notable is South Korean researcher Hwang Woo, who in 2005 claimed to have developed a remarkably efficient cloning technique, but who was later discovered to have fabricated almost all his human cloning research.

Investigation committees found that Hwang not only faked his results, but also used a much larger number of eggs than he originally reported. According to some news reports, Hwang obtained some eggs unethically, coercing junior scientists to donate. And some women donated eggs multiple times, despite adverse reactions and medical risk.

Unlike other types of human research, there are no U.S. federal guidelines governing how these experiments should be carried out. President Bush severely limited federal funding for embryonic stem cell research in 2001, including all research involving the creation of new stem cell lines. This has meant that the National Institutes of Health, the nation's largest source of biomedical funding, has not played its normal regulatory role, and individual states and research institutions have had to pick up the slack. "If there were agreed-upon national standards, it would probably speed up much of this protocol approval process," says Arnold Kriegstein, director of UCSF's stem cell program.

Both Massachusetts and California, the latter via the California Institute of Regenerative Medicine, have recently enacted rules governing embryonic stem cell research. Both sets of guidelines prohibit paying egg donors, but do allow compensation for direct expenses, such as childcare and transportation. California takes it one step further, allowing women to be paid for time off work. It's unclear if Massachusetts law permits this practice.

David Magnus, a bioethicist at Stanford University, says these regulatory systems lack adequate monitoring mechanisms, though. "I think it would be an advantage to think about ways to make sure researchers are doing what they say they are going to do," says Magnus. "I would guess that we won't see problem with the first few institutions, which have been very careful. Problems would more likely occur down the road, when [nuclear transfer research] starts to become routine."

While some research suggests that the tricky cloning procedure will require fresh eggs, two teams of scientists are trying another alternative. Rather than using freshly donated eggs, researchers at the University of California, San Francisco and Daley at Children's Hospital are using so-called fail-to-fertilize oocytes, eggs that failed the in vitro fertilization process and were donated to medical research. Fail-to-fertilize oocytes are likely to be easier to come by than freshly donated eggs, and therefore could allow scientists to test and refine their cloning methods.

But whether that method will solve the egg-donation problem facing stem cell researchers is unknown. "It may be that we need fresh oocytes," says Daley.