Controversial payments to women who donated eggs for stem-cell research took place before South Korea adopted its first bioethics law in January banning a financial reward for such donors.

Speaking at a news conference, Roh Sung Il, head of Miz Medi Hospital in Seoul, said he had worried that what he was doing might be seen as controversial and kept his transactions from other researchers, including Hwang Woo Suk, a cloning scientist who runs the world's most successful human embryonic stem-cell laboratory.

Despite repeated questions from journalists, Roh refused to clarify another crucial question: whether junior scientists on Hwang's team volunteered to donate eggs -- an ethics violation, critics say, given a hierarchical lab culture in South Korea.

"It was difficult to obtain enough eggs for our research. It was inevitable to offer some compensation in return for egg donations," Roh said. The doctor said he paid 1.5 million won, or $1,440, per woman.

'One of Humankind's Biggest Dreams'

"I made a difficult decision hoping that it would help pave the way for a breakthrough in fulfilling one of humankind's biggest dreams, which is to find remedies for hard-to-cure diseases," Roh said, fighting back tears. "I did not discuss my decision with Dr. Hwang because I thought I should take all responsibility myself."

The eggs obtained through Roh were used for Hwang's research, which was recognized in 2004 as the first successful attempt to clone human embryos and harvest stem cells from them.

Paying Women for Donating Eggs

In theory, stem cells can grow into tissues in any parts of the human body.

Cloning them is a milestone in the quest to grow patients' own replacement tissue to treat diseases such as Alzheimer's disease, diabetes and spinal cord injuries. The process, however, takes dozens of eggs to make one cloned human embryo.

The embryo, considered a life form by many, is destroyed in the process of harvesting stem cells.

A debate in the United States and elsewhere over the ethics of paying women for donating eggs for such a process is likely to escalate with Monday's revelation in South Korea.

Roh's transactions took place before South Korea adopted its first bioethics law in January banning a financial reward for egg donors.

Ethics Crisis

In April, the National Academies of the United States recommended against payments for human eggs beyond expenses incurred by the donors. Roh also said his payments were meant to compensate the loss of work and other inconveniences the women suffered. But critics still consider such payment unethical.

The ethics crisis in Hwang's lab erupted a week ago when a University of Pittsburgh biologist, Gerald Schatten, ended his 20- month-old association with Hwang, saying he had evidence that Hwang's eggs were obtained unethically.

With Hwang delaying clarifications, MBC, a leading television network in South Korea, said Monday that some of the eggs Hwang's team had used were acquired from women who were in debt and sold their eggs for money.

MBC planned to broadcast its interviews with the women on Tuesday.

MBC also quoted a woman as saying that she did not know whether her eggs would be used in stem-cell research, an allegation Roh vehemently denied Monday. Roh said all egg donors were properly informed.

Some fear that the uproar will hamper stem-cell research in South Korea.