US scientists say they have developed a way of harvesting stem cells without destroying the embryo they grow in.
Stem cells can be programmed to become many kinds of tissue
The Massachusetts-based Advanced Cell Technology removed embryonic stem cells from mice embryos with no apparent damage, the journal Nature said.
Scientists believe it would sidestep some of the ethical objections to stem cell research if repeated in humans.
But campaigners said they still had concerns and urged scientists to concentrate on other areas.
Stem cells are "master" cells that can become many kinds of tissue.
Those harvested from early-stage human embryos are thought to hold the most potential for research, as they have the ability to become almost any kind of adult cell in the body.
Stem cells from adult tissue have some, but not all of this ability.
However, use of embryonic stem cells is opposed by many on the grounds that it involves destroying an embryo.
Lead researcher Robert Lanza, of Advanced Cell Technology, said the new technique could allow scientists to create a bank of personal cells for children before they are born to treat diseases later in life.
And he added it might provide a way of diffusing the row over the ethics of embryonic stem cell research.
"The most basic objection to embryonic stem cell research is the fact that embryos are deprived of any further potential to develop into a complete human being.
"We have shown in a mouse model that you can generate embryonic stem cells using a method that does not interfere with the developmental potential of the embryo."
In the study, researchers removed stem cells from mice embryos and then placed them in a culture where they developed into fresh colonies of master tissue.
Nearly half of the 47 embryos developed into healthy pups - broadly the same as the control group.
The study is set to be discussed at the American Society for Reproductive Medicine conference in Montreal on Monday.
Professor Richard Gardner, chairman of the Royal Society's working group on stem cells research and cloning, said: "The idea that ethical fears will be allayed is a red herring.
"It is difficult to see any parent willing to risk having cells extracted from their own child while it is an embryo, unless it is to create stem cells in case that particular child needed them in the future."
Meanwhile, a separate study in Nature by a team at the US Whitehead Institute for Biomedical Research is also being touted as another way round the ethical concerns.
By modifying DNA, researchers were able to create an embryo in mice trials which could never develop in the womb but could still be used to get stem cells.
The scientists said the embryo could not be regarded as a potential life.
But Josephine Quintavalle, of the UK-based Comment on Reproductive Ethics, said neither technique answered their concerns.
"On the first one, there is no evidence yet that taking stem cells will not cause harm later on.
"Both still interfere with the natural process, and you have to ask why someone would want these stem cells.
"I think scientists would be far better to concentrate on other areas of stem cell research such as amniotic and adult stem cells which show far more promise."