Embryonic stem cell researchers are worried about the future of international cooperation in their field after a prominent scientist's surprise resignation from a fledgling stem-cell-sharing effort.

On Thanksgiving, South Korean scientist Woo-suk Hwang of Seoul National University resigned as head of the World Stem Cell Hub, a nascent international embryonic stem cell research effort he started. In 2004, Hwang's team was the first to clone human embryonic stem cells, master cells from which specific kinds of tissue arise.

Since then, Hwang's team has become the world's leader in stem cell research. This year, it unveiled 11 more cloned stem cell lines, and it cloned a dog.

But a team member, the University of Pittsburgh's Gerald Schatten, resigned this month. He warned of ethical breaches involving junior lab members inappropriately donating eggs for research.

Donor eggs are combined with skin cells in the cloning process. Hwang's 2004 paper said all eggs had been freely given by anonymous donors. But he acknowledged that a team doctor paid 20 women about $1,400 each to donate eggs. Hwang also confirmed Schatten's charges. Hwang acknowledged that he did not disclose these breaches upon learning of them.

"No question that people are taking a step back from interacting with the Hub," says Leonard Zon, former president of the International Society for Stem Cell Research. "It remains for Dr. Hwang's colleagues to prove the future of the Hub can be maintained."

The organization will outline new ethics guidelines this week.

Paul Root Wolpe of the Center for Bioethics at the University of Pennsylvania points out that Hwang did not resign because he used eggs from his researchers but because he lied about it and brought shame "in a country where public shame is so powerful."

He is not the only one to note that Hwang's findings have not been compromised. "While ethical issues about (egg) donation should be debated and the process regulated, the scientific conclusions of Dr. Hwang's research remain intact," Schatten said in a statement.

The South Korean government says it will still pay for Hwang's work, and thousands of women have since offered their eggs, according to news reports.

"Korean bioscientists have opened a new era with cutting-edge technology, but I don't think there is any bioethics relevant to that at this moment here," says theologian Heup Young Kim of South Korea's Kangnam University. "We have our different social and cultural context, so we have to formulate our own bioethics."

One irony of Hwang's resignation is that South Korea's egg donation standards, and those of Hwang's lab, are now stricter than U.S. standards, says bioethicist Insoo Hyun of Case Western Reserve University in Cleveland. The lab requires consent forms and psychological evaluations for donors. And earlier this year, South Korea outlawed paying for eggs, which is legal in the USA.

Stem cell researchers hope to create replacement tissues to treat diseases such as diabetes and Parkinson's. Opponents assail the destruction of embryos involved in gathering the cells. President Bush has restricted research money.

"I would hate to see the United States get on an ethics high horse as if we are moral and other countries such as Korea are not," says the Rev. Ronald Cole-Turner of Pittsburgh Theological Seminary.

"Which society is the more ethical?" he asks. "The one that at least has a standard or the one that can't find a reasonable degree of compromise to create a standard?"