Human embryonic stem cell lines have been generated without embryos being destroyed, according to researchers.
The scientists removed single cells from the embryos
A US team created the lines by removing single cells from embryos, a process that left them intact, they report in the journal Nature.
At present, growing this type of stem cell results in embryo destruction.
The researchers say their findings may remove some of the ethical barriers to this field and provide a way of bypassing current US legislation.
In 1995, the US Congress passed an amendment stating that the government would not fund research in which human embryos were destroyed.
And in 2001, President George W Bush declared federal funding would only be available for research using the 61 human embryonic stem cells lines already in existence, where a "life or death decision had already been made".
This meant no funding for the creation of new lines - whether from existing embryos or cloned embryos.
US stem cell researchers said the funding limits had ensured the US lagged behind in this field of research, limiting new studies to private companies, while pro-lifers hailed the decision.
Scientists believe stem cells may one day help to combat a range of diseases, such as Alzheimer's or Parkinson's disease, or to repair spinal cord injury.
A spokeswoman for Mr Bush described the new approach as encouraging.
But the BBC's James Westhead, in Washington, says it is not yet clear whether the new technique gets around the funding restrictions.
Supporters argue the research could save many lives
Questions about its effectiveness, and whether it really is a more ethically acceptable approach, means this is unlikely to herald the end of the deeply divisive debate, our correspondent says.
Professor Robert Lanza, medical director of Advanced Cell Technology (ACT) in Massachusetts, US, and lead author on the paper, said: "We have shown for the first time you can create human embryonic stem cells without destroying the embryo and thus without destroying its potential for life."
Using spare human IVF embryos, the researchers removed single cells from them, employing the same procedure used for pre-implantation genetic diagnosis (PGD), a technique that has been used in IVF so cells can be removed from the embryo and tested for genetic disorders.
The process, said the team, leaves the embryo intact, enabling it to continue and grow into a healthy foetus.
Of the 16 embryos used, they developed two long-term stem cell lines, which, Professor Lanza said, were "genetically normal and able to generate all of the cell types of the body".
If the research is successfully replicated by other scientists, this could mean more stem cell lines for research and potentially tailored stem cell lines which could be used for children born through PGD.
David Christensen, from the Family Research Council - a US-based conservative group, said the research "shows many more researchers are seeing that we need alternatives to destroying human embryos to get stem cells".
"Unfortunately what Professor Lanza did was entirely unethical because he generated and manipulated 16 human embryos and then threw them all away," he added.
Other scientists said while the paper marked a technical achievement, they were concerned about its practical relevance.
Professor Robin Lovell-Badge, at the UK's MRC National Institute for Medical Research, said: "I am also unconvinced by the ethical arguments - spare IVF embryos used to derive ES cell lines would have been destroyed anyway."
Professor Chris Shaw, a neurologist at the Institute of Psychiatry, King's College London, said: "This is a useful alternative source for embryonic stem cells but it side-steps the crucial ethical question: 'What happens to those embryos found to have a genetic mutation and those that are healthy but excess to requirement?'"