American stem-cell researchers have been warning for years that their work is being stifled by restrictions while scientists abroad forge ahead. In 2004 that warning hit home when a breakthrough emerged from South Korea.

On February 12, Woo Suk Hwang and Shin Young Moon of Seoul National University announced that they´d done what biologists had previously found impossible: they had turned an adult cell into a brand-new human embryo-cloning a human being to harvest stem cells. The team injected the DNA from the adult cell into an egg whose own DNA had been removed and then stimulated the egg to divide. From the resulting embryo, they plucked and grew embryonic stem cells.

Both in the womb and in the lab, embryonic stem cells show an astonishing ability to grow into bone, muscle and almost every other cell type. Scientists hope to treat disease by creating embryonic stem cells from a patient´s own body and coaxing them to grow into tissues or organs that, because they would be a perfect genetic match to the person´s own, could be transplanted without the problem of rejection.

Key to the Koreans´ success was having a supply of more than 240 eggs from 16 female volunteers with which to fine-tune the process. U.S. researchers, in contrast, are hampered by President George W. Bush´s 2001 ban against using federal research funds to work with new stem-cell lines.

The same moral objections to creating and destroying human embryos that guided Bush´s decision have also been raised in the U.K. In August, though, British authorities decided that pursuing potentially life-saving therapies was the greater moral imperative, and awarded the first license to clone human embryos for research.

U.S. scientists are left frustrated. â€There´s a lot of pride in American science, and we don´t like the idea of seeing the cutting edge moving to other nations,†says cell biologist Larry Goldstein of the University of California at San Diego.

Deprived of federal support, U.S. scientists have turned to unlikely benefactors. In November, California voters approved a ballot initiative that will direct $3 billion over 10 years to embryonic stem-cell research. Even with new sources of funding, though, there´s no guarantee that embryonic stem cells will perform the miracles expected of them. Scientists have yet to figure out how to transform the cells into tissue types, how to prevent them from multiplying wildly into cancers-and whether the new tissues will cure disease. These laborious steps will take a minimum of five years, experts say. â€But the fewer restrictions we have,†notes neuroscientist Pantelis Tsoulfas of the University of Miami, â€the faster we´ll find out what these cells are useful for.â€