An ethics crisis at one of the world's most successful human embryonic stem cell laboratories has plunged the controversial field of research into a new swirl of uncertainty. The accusations surrounding Korean cloning expert Woo Suk Hwang of Seoul National University--the first scientist to grow stem cells inside cloned human embryos--has already killed a spate of planned studies that sought to prove the cells' medical potential. The claims that Hwang may have obtained human eggs for his studies from women who felt pressured to donate are also reigniting a long-smoldering debate in the United States over the ethics of paying young women for their eggs, which are difficult to obtain but essential to the production of stem cells tailored to individuals. Egg donation, which is generally safe but occasionally leads to serious and even life-threatening complications, has been a wedge issue in the stem cell debates, linking feminists and other liberal thinkers to conservatives who favor tighter limits on stem cell research. 'We're in danger of making women into guinea pigs for this research even before there are any treatments to be tested,' said Marcy Darnovsky, associate director of the Center for Genetics and Society in Oakland, Calif. 'We really need clear rules that someone is enforcing.' With current techniques, it takes dozens of eggs to make a single cloned human embryo, which is destroyed in the process of extracting the stem cells. That means that if the field of therapeutic cloning is to advance--a field involving the creation of cloned embryos as sources of stem cells that would be genetically matched to particular patients--a significant number of eggs will be needed both to fuel the initial research and eventually to satisfy the demands of patients. Scientists at Advanced Cell Technology of Worcester, Mass. , made the decision to pay women only after a long analysis by an ethics board created by the company, said scientific director Robert Lanza. He still thinks it is the right way to go, Lanza said, given the painful injections involved, the uncomfortable egg suction procedure, and the approximately 5 percent chance of a serious case of hormonal over-stimulation, which can require hospitalization. Others say such payments cannot help but be coercive, especially for poor women who might feel compelled to take on those risks just to make ends meet. In April, the National Academies, chartered by Congress to advise the nation on matters of science, released a report that recommended against payments for human eggs beyond expenses incurred by the donors, in part because of the 'sensitivities' inherent in the creation of embryos destined for destruction. But the report's impact remains uncertain as research institutions, fertility clinics and the biggest wild card of them all--Congress--mull the Academies' findings. What can we learn from the opening paragraph?