After a year and a half of denials, Woo Suk Hwang admitted last Thursday that his stem-cell research used eggs from paid donors and junior members of his team. Although planning to continue his research, Hwang said he would quit his other positions.

Despite the confession, which shocked South Korea and the global stem-cell research community, many have remained supportive. The Korean government has promised to continue his funding at Seoul National University, and nearly 800 women have signed up to donate eggs to his research through a non-profit foundation. But critics are pushing for a deeper investigation into what happened.

The eggs in question were used in the first successful attempt to derive stem cells from a cloned human embryo (W. S. Hwang et al. Science 303, 1669–1674; 2004). The study was hailed worldwide. But three months later, Nature reported claims from one of Hwang's graduate students — later retracted — that she and another junior researcher in the lab had donated eggs (see Nature 429, 3; 2004). The controversy was reignited last month, when the fertility doctor who supplied Hwang with eggs, Sung Il Roh, admitted to paying at least 20 women for their donations.

Egg donation is invasive and painful, and can have serious side effects. Paying donors is now illegal in Korea, although it was not at the time of Hwang's study. And receiving donations from subordinates raises a variety of ethical problems, including the spectre of coercion.

Hwang has a credibility issue now. The dust hasn’t settled.

Until 24 November, Hwang had denied everything. Then, in a press conference aired live on all three of the country's main television networks, he admitted that eggs from his researchers and paid donors had been used. A downcast Hwang told the Korean media that he had lied about the researchers' donations to protect their privacy. “I am so ashamed. I will not attempt to justify what I did,” he said.

Critics are still concerned, however (see page 532). Young Mo Koo, a bioethicist at Korea's University of Ulsan, says Hwang has not addressed enough questions about his involvement with the egg donors: “There needs to be an investigation by an independent party.”

For example, Hwang claims to have known nothing of the payments until a few days before his confession — when Roh told him. Yet in April 2004 he told Nature that he had himself “arranged” many of the donors at the hospital concerned. Roh was awarded 40% of the patent resulting from the paper, on which he was not an author. He says he does not know why Hwang offered him so much but that it was not compensation for providing the eggs. “I don't need any rewards,” he says. Hwang has not disclosed his expenditures or budget for the project, saying only that all funds came from private sources.

The extent to which a junior member of his laboratory might have felt pressure to donate is also under debate. The student spoken to by Nature last April showed no signs of having been coerced by Hwang. During a 28-minute interview, she proudly described how her patriotism and concern for those with spinal injuries had inspired her to donate. Nature was unable to contact the other researcher, who is since thought to have moved to the United States. But according to Roh, she felt obliged to donate after making mistakes early in the experiment that wasted eggs and set the team back by months. “I think it's a beautiful story,” Roh told Nature, referring to both women's donations.

Insoo Hyun, a bioethicist at Case Western Reserve University in Cleveland, Ohio, has worked with Hwang's group on bioethics protocols. Hyun says the students' accounts prompt hard questions about what coercion is. “To some degree, in Korean society, if you make a mistake you must make good on it somehow,” he says. “It's a grey area.”

Woo Suk Hwang admits to the world that he used eggs donated by his juniors. Credit: J.-M. LEE/AP

Many Koreans have already sided with Hwang. On 26 November, demonstrators gathered outside the Munhwa Broadcasting Company in Seoul to decry the firm's lack of patriotism after it aired evidence that Hwang had lied. Eleven out of twelve advertisers have dropped their contracts with the company, according to the JooAng Daily.

Although Hwang has promised to resign his directorship of the Seoul-based World Stem Cell Hub, the international cell-sharing initiative says it will hold his position for him.

Some stem-cell researchers and potential collaborators in other countries also seem willing to forgive and forget. One US scientist, who would not speak on the record for fear of appearing insensitive to ethical issues, says it is hypocritical to punish Hwang for paying donors when infertile couples in the United States often pay tens of thousands of dollars for eggs. “Is it OK to buy them for one purpose and not another?” he asks.

The fact that Hwang lied may make it hard for him to regain his international prestige. “Now it becomes an issue of whether one has a collaborator whose integrity one can trust, and that is a very fundamental issue,” says Evan Snyder, a neuroscientist at the Burnham Institute in La Jolla, California, who has suspended plans to work with with Hwang. Hyun agrees: “Hwang has a credibility issue now. The dust hasn't settled.”

“It's a useful cautionary tale,” adds Larry Goldstein of the University of California, San Diego. He argues that the community should create a set of international ethical guidelines to protect patients and donors.