The resignation of South Korean stem cell pioneer Hwang Woo-Suk last week after he admitted to unethical conduct has left international researchers reiterating the need for stringent regulation of the field.

Hwang, who conducts his research at Seoul National University, admitted on Thursday (November 24) that two women working in his lab as junior scientists had given their eggs for stem cell research in 2002 and 2003, a fact he had been aware of—but denied--in May 2004.

According to reports from Korean news outlets, Hwang told a press conference that, to take full responsibility for the scandal, he would resign from "all posts," including leading positions at the Seoul stem cell team and the World Stem Cell Hub, which opened last month. He said he would, however, continue his research.

"I am very sorry that I have to tell the public words that are too shameful and horrible," he was quoted as saying by the BBC. Hwang said the staff donations had taken place without his knowledge, when the researchers suggested making voluntary donations to ease ova shortages. "I clearly turned it down." Hwang said at the press conference that he later learned that the women had donated the eggs under false names.

After Hwang and his colleagues announced in 2004 that they had derived stem cells from a cloned human embryo, reports surfaced that a Ph.D. student from Hwang's lab and another junior colleague donated eggs for the experiments. The student later retracted her statement and Hwang and a colleague denied that any lab members had donated eggs.

Hwang said he lied because of a "strong request by the researchers to protect their privacy," at the press conference, according to the BBC. The donations did not break any laws in South Korea, officials said.

Hwang could not be reached for comment by deadline. The Korea Heraldreported on Monday that he had left the city temporarily.

The news looked likely to have a negative impact on already-shaky collaborations between South Korean researchers and some of their international colleagues. On November 12, Gerald Schatten from the University of Pittsburgh ended a 20-month collaboration after learning that Hwang had "misrepresented" facts about where donated oocytes had come from. Schatten declined to comment to The Scientist, but other representatives of institutions such as Harvard and the University of California, San Francisco, told The Scientist at the time they would also be hesitant to collaborate with Hwang.

In Britain, stem cell researcher Stephen Minger said that the incident demonstrated the value of stringent ethical regulation such as what the Human Fertilization and Embryology Authority enforces in the UK. "Under HFEA licenses you have to account for everything—every egg, every embryo," he told The Scientist. "We have to file a new report every six months detailing where they all came from and what happened to them."

Minger acknowledged that Hwang "did not show good judgment" in the incident, but added "his international reputation as a scientist remains untarnished. He's clearly the leader in the field [and] I would continue to work with him."

"I agree that the guy has had a rough deal," Chris Shaw, professor of Neurology at Kings College London told The Scientist. "The mistake is that he didn't confess immediately after discovering that women in his labs were donating eggs - but it won't be the first time that a scientist has lied to journalists - and he has not lied in his scientific papers."

Support for the researcher among his fellow South Koreans has proven strong. On Sunday night, some 100 or more advocates held a vigil in front of the MBC-TV television channel building, threatening to boycott advertisers on the channel, which had broadcast a program questioning the source of the eggs used in his research, the Korea Herald reported. The paper also reported that more than 700 women had expressed a wish to donate ova since the launch of a private foundation last Tuesday to facilitate legal and ethical donations of human eggs for research purposes.