Using high-powered microscopes and ultrathin glass filaments, workers dressed in space suits and white caps gently squeeze out the contents of a tiny cell and fill it with material from another.
This is no ordinary laboratory. It was there, in Building 85 at Seoul National University, that Drs. Woo Suk Hwang and Shin Yong Moon created human embryos through cloning and extracted embryonic stem cells from one of them.
Their work, to be published on Friday in the journal Science, has shaken the scientific world and reignited debates over the ethics of human cloning.
Dr. Hwang, 50, an expert in animal cloning, has a knack for choosing high-profile projects. In December, he gained notice abroad after reporting that he had cloned cattle resistant to mad cow disease. In 1999, he began a project to save endangered tigers through cloning. He works virtually nonstop most of the week, catching sleep when assistants drive him to slaughterhouses and ranches, his workers say.
''If we were an army and Dr. Hwang was a general, he can be described as a leader who sets examples by actions rather than words,'' said Dr. Lee Byeong Chun, an associate professor at the university who works under Dr. Hwang. ''He's always delivering lectures to farmers, as well as officials in high positions, about the latest technology.''
Dr. Moon, 56, an expert on female infertility, heads the South Korean Stem Cell Research Center that the government formed in 2002 to apply stem cell research to treat diabetes, heart disease and other diseases. Among its goals are developing technology to raise human embryonic stem cells and to form a genetic database based on the findings. The center is also developing a set of ethics for stem cell research.
As in the United States, human cloning is a focus of heated debate here. When scientists at Kyung Hee University announced in 2001 that they had begun research on human cloning, Korean religious and civic groups mobilized to stop such research.
Late last year, the government adopted a law barring cloning for reproduction. Experiments that use embryonic stem cells have to receive reviews and authorizations from a government ethics panel. Further regulations are to take effect next year.
Seo Jae Chul of Green Korea, an environmental group that has joined with others to oppose human cloning, said the new findings caught opponents by surprise. ''Dr. Hwang's research had not been scrutinized by social groups, since he had been involved in animal research,'' Mr. Seo said.
Mr. Seo added that sensitivity to human medical experimentation seemed less acute in South Korea than in the West.
''The Western world, especially Europe, experienced the atrocities of the Nazis,'' he said. ''Here, there is no such experience.''
Drs. Hwang and Moon have emphasized that their aim is not to create carbon copies of humans, but to advance research into the nature and treatment of diseases.
The government, which provides $7.8 million a year for stem cell research, financed their work. Research organizations at universities like Seoul National also receive money from large companies and other private donors.
Mr. Seo says the country needs to temper the speed of research and development arising from the rapid industrialization that has enabled the country to emerge from the ruins of the Korean War to become the 12th largest economy in the world.
''The fact remains the same,'' Mr. Seo said. ''They've opened a Pandora's box. Who can say for sure that this technology will never be abused? One thing for sure now is that we will call for deep scrutiny on this matter.''
