"This is truly the Holy Grail: To be able to take a few cells from a patient -- say a cheek swab or few skin cells -- and turn them into stem cells in the laboratory," said Robert Lanza of Advanced Cell Technology.

"This work represents a tremendous scientific milestone - the biological equivalent of the Wright Brothers' first airplane."

"It's bit like learning how to turn lead into gold."

Research in the field has been highly controversial as human embryos have been the main source of stem cells.

Some see the destruction of a viable embryo as unacceptable -- one reason why the US president has banned Federal funding for research employing embryonic stem cells.

Scientists have also come up against problems finding women willing to donate eggs -- all of which has posed problems for those wanting to carry out research.

But this new technique could do away with such obstructions -- so much so that cloning pioneer Ian Wilmut is abandoning cloned embryos.

"The fact that the introduction of a small number of proteins into adult human cells could produce cells that are equivalent to embryo stem cells takes us into an entirely new era of stem cell biology," he said.

But some researchers are sounding a note of caution.

"This new research is just the beginning -- we hardly understand how these cells work," said James Thomson of the University of Wisconsin at Madison, one of the scientists behind the new breakthrough.

"It is not the time to abandon stem cell research."