US scientists believe they have found a less controversial way of creating embryonic stem cells by using skin cells to create a "hybrid" version.
Stem cells can be programmed to become many kinds of tissue
The Harvard University team fused lab-grown embryonic stem cells with the adult cells to create the new stem cell, Science will report this week.
Researchers believe these hybrid embryonic stem cells could help disease research without using human embryos.
But UK experts warned the hybrid stem cells were not a perfect match.
Stem cells are "master" cells that can become many kinds of tissue.
Those harvested from early stage human embryos have the potential to become any kind of cell in the body.
Scientists hope that replacement tissue made from stem cells will one day be used to treat a host of diseases, including currently incurable conditions such as Parkinson's and diabetes.
The authors reported: "The hybrid cells had the appearance, growth rate, and several key genetic characteristics of human embryonic cells.
"They also behaved like embryonic cells, differentiating into cells from each of the three main tissue types that form in a developing embryo."
And they added the new technique "may circumvent some of the logistical and societal concerns" that have hampered research.
But they admitted it would be years before the technique could be used in research.
Critics of embryonic stem cell research have argued it is not ethical to create human embryos for stem cells only to destroy them.
This method uses existing stem cells to reprogramme the skin cell.
Professor Ian Wilmut, who cloned Dolly the sheep, from the Centre for Reproductive Biology at the University of Edinburgh, UK, pointed out that the newly generated cells had twice the normal number of chromosomes.
He said at present there was no known way to remove the chromosomes that were not wanted.
But he added: "The important use of this approach is to study the mechanisms that cause a cell to change from one type to another, the process that involves 'nuclear reprogramming'."
And he said the findings should not deter the scientific community from carrying on using current techniques for disease research.
Professor Miodrag Stojkovic, deputy director of the Centre for Stem Cell Biology and Developmental Genetics at the University of Newcastle, UK, said: "This is interesting research which will help us understand how the nuclei of adult cells can reprogram.
"However, these cells would not be useful for stem cell treatments, because they are abnormal. These cells have 92 chromosomes rather than the normal 46."