One man is an American. The other is from South Korea. They called each other "brother" and, in the laboratory, they seemed kindred spirits.

But the relationship between University of Pittsburgh reproductive biologist Gerald Schatten and Seoul National University veterinarian Hwang Woo-suk unraveled rapidly and publicly over the last three months, as details emerged that the cloned human stem cell lines Dr. Hwang claimed to have created were all phony.

A Pitt investigatory panel last week said Dr. Schatten, who co-authored a paper last year in the journal Science announcing the discovery, was not guilty of scientific misconduct and had not known about the fraud. But the episode nonetheless has become a cautionary tale regarding the pitfalls of international scientific collaboration.

More than ever before, science recognizes few borders, as scientists migrate to nations where certain types of research are permissible or more easily performed than in other nations and as the Internet has made collaborations over long distances possible.

Human embryonic stem cell research is a prime example of this phenomenon. In the United States, federal restrictions make it difficult for scientists who receive federal funding, such as Dr. Schatten, to study human embryonic stem cells. Some states, including Pennsylvania, have outright bans on the creation of human embryonic stem cell lines.

Other nations, however, including the United Kingdom and South Korea, have embraced human embryonic stem cell research.

"We're looking now at a global scientific community that is not only collaborating but in some ways is in competition on an international level," said Dr. William Hurlbut, a bioethicist at Stanford University and a member of the President's Council on Bioethics.

In human embryonic stem cell research in particular, some nations are pressing ahead with research in hopes of becoming leaders in potentially lucrative stem cell therapies, which have been proposed for treating Parkinson's disease, diabetes and other disorders.

But cultural, ethical and language divides remain and can make international collaborations difficult, Dr. Hurlbut said. "This is becoming an international problem," he added, noting that stem cell therapies clinics have begun popping up in countries such as Costa Rica, China and Russia.

When Dr. Schatten and Dr. Hwang began working together in December 2003, the collaboration was mutually beneficial. As detailed in the Pitt panel's report last week, Dr. Hwang claimed to be the first to clone a human embryo and derive stem cells from it, but his initial attempt at publication in the prestigious journal Science had been rejected.

Dr. Schatten, on the other hand, had been unsuccessful in his attempts to clone monkeys and his work on human embryonic stem cells had been limited to studies of the handful of existing stem cell lines approved by the U.S. government.

Dr. Schatten helped Dr. Hwang revise his report and urged Science editors to accept it. Its subsequent publication in the spring of 2004 established Dr. Hwang as one of the world's leading embryonic stem cell researchers, while Dr. Schatten enjoyed access to the South Korean's techniques, which he hoped to adapt for his monkey cloning studies.

The sort of aid extended by Dr. Schatten to Dr. Hwang is quite natural among scientists, said Dr. Robert Lanza, an embryonic stem cell researcher at Advanced Cell Technologies in Worcester, Mass. "You feel badly when something doesn't get printed in the right journal because of language problems or because it isn't presented right," he said.

But he predicted scientists now will take greater care in signing on as authors of such papers, given the blow Dr. Schatten's reputation took from Dr. Hwang's fraud. "This was definitely a warning flag," he added.

These long-distance relationships are "collaborations of a strange sort," Dr. Hurlbut said. It is difficult for international collaborators, particularly in countries as distant as South Korea and the United States, to fully understand and monitor what is going on in each other's laboratories, he explained.

Dr. Arthur Caplan, director of the Center for Bioethics at the University of Pennsylvania, isn't sure the Korean stem cell fraud is necessarily a cautionary tale for international collaborations.

"You don't expect your international collaborator to make it all up any more than you would your collaborator down the street," he said.

"The internationalization of research does raise questions about whose rules, whose standards, do you follow?" Dr. Caplan acknowledged. Different countries might have different standards for informed consent of individuals receiving experimental drugs, for instance, or might have different ethical restraints on how women donate eggs for research, or whether they should be compensated.

It's a phenomenon that Dr. Hurlbut has called "outsourcing ethics," pushing research that might be considered unethical in the United States -- such as human embryonic stem cells -- to countries where standards are different.

"Think of the commercial advantage the Chinese would have if they had lower standards" for performing new drug trials, he said.

Often as not, however, these differences in standards end up placing people outside the United States at risk. In the mid-1990s, for instance, the National Institutes of Health performed a study of the AIDS drug nevirapine in Uganda that later was shown to have violated federal patient safety rules.

In 2004, leading AIDS researchers protested a federally funded AIDS vaccine trial in Thailand, arguing that it combined two antiquated vaccines that already had been proved ineffective.

"This is going to be a big problem globally," Dr. Hurlbut said, though he hopes the Korean stem cell scandal will draw greater attention to the need to develop better standards for international collaborations.

In the case of embryonic stem cells, he said he hopes it also will encourage U.S. officials to pursue research avenues that will create less pressure to move research overseas.

Dr. Hurlbut is a proponent of so-called "altered cell nuclear transfer," which could produce stem cells from human eggs genetically altered so that they could never develop into individuals. He argues this approach sidesteps the need to destroy viable human embryos to obtain embryonic stem cells.

"I think this is a sobering moment for anyone engaged in complicated collaborations," agreed Ronald Cole-Turner, a bioethicist at the Pittsburgh Theological Seminary. But he said critics of human embryonic stem cell research such as Dr. Hurlbut should take care in the restrictions they put on U.S. researchers.

"Sometimes we put constraints on them and then blame them for failures caused by those constraints," Dr. Cole-Turner said. Dr. Schatten, for instance, was limited in how deeply he could be involved in Dr. Hwang's lab because of federal and state restrictions on human embryonic stem cells and that could have contributed to his failure to recognize the fraud.

Questions also arose about which institutions needed to oversee the work. For example, Dr. Schatten apparently talked to his bosses at Pitt before accepting Dr. Hwang's offer of senior authorship of the stem cell paper. But it's not clear what they expected he should know about experiments that were being conducted overseas.

Also, the role the university's institutional review board played in Dr. Schatten's collaboration is unclear. American researchers must share study plans that involve human subjects with the review board, which makes sure that participants are volunteering for experiments and will not be endangered in them.

A letter from Pitt's institutional review board ultimately concluded that its approval was not necessary because the project didn't involve human subjects at Pitt.

Curiously, the letter, which was sent to Dr. Schatten and made available in supplemental materials provided by Science, was dated the day after the stem cell paper was submitted to the journal for review, and therefore after the experiments were complete.

Dr. Cole-Turner said the rules need to be clear, but care also must be taken to ensure that scientists are unnecessarily restricted in working with distant colleagues.

"They collaborate, but not deeply enough," he said. "We put [scientists] at risk" when regulations are too strict. "I think we need to recognize that."