Scientists say they have created a stem cell line from a human embryo that had stopped developing naturally, and so was considered dead. Using such embryos might ease ethical concerns about creating such cells, they suggested.

One expert said the technique makes harvesting stem cells no more ethically troublesome than organ donation. But others said it still carries scientific and ethical problems.

Scientists want to use human embryonic stem cells to study diseases and create transplant tissue for treating illnesses such as diabetes and Parkinson's disease. Such cells are taken from human embryos that are a few days old, and the harvesting process destroys the embryo. That raises ethical objections.

The new work, published online Thursday by the journal Stem Cells, comes from Miodrag Stojkovic of the Prince Felipe Research Center in Valencia, Spain, with colleagues there and in England.

They studied embryos donated by an in vitro fertilization clinic with consent of the patients. Part of the work focused on 132 "arrested" embryos, those that had stopped dividing for 24 or 48 hours after reaching various stages of development.

Thirteen of these embryos had developed more than the others, reaching 16 to 24 cells before cell division stopped. Scientists were able to create a stem cell line from just one of these embryos.

These stem cells performed normally on a series of tests, Stojkovic said in a telephone interview.

He said he did not know whether the result indicated a solution to ethical concerns about embryonic stem cells. The point of the research was to show that such embryos provide an additional source of the cells beyond healthy embryos, rather than to set up any kind of a competition, he said. Both sources should be used, he said.

Dr. Donald W. Landry, director of the division of experimental therapeutics at the Columbia University Medical Center in New York, who proposed the idea of getting stem cells from arrested embryos in 2004, called the work an important addition to the field.

"Regardless of how you feel about personhood for embryos, if the embryo is dead, then the issue of personhood is resolved," Landry said.

"This then reduces the ethics of human embryonic stem cell generation to the ethics of, say, organ donation. So now you're really saying, `Can we take live cells from dead embryos the way we take live organs from dead patients?"'

Landry is part of a consortium that is pursuing the approach.

But others said the approach fails to solve the ethical problems.

There is no way to prove that an arrested embryo would have stopped growing if it had been put into a woman's womb rather than a lab dish, said Robin Lovell-Badge of the Medical Research Council's National Institute for Medical Research in London. So that leaves open the possibility that it was the lab conditions that halted their growth, he said.

The Rev. Tad Pacholczyk, director of education for the National Catholic Bioethics Center in Philadelphia, said he believed an embryo may not be dead if individual cells are still alive and able to create stem cell lines.

Landry says an embryo is dead if its cells irreversibly stop working together to function as a single organism. But even under that definition, Pacholczyk said, scientists know too little about early embryos to discern when one is truly dead.

Dr. George Daley of the Harvard Stem Cell Institute said the new paper's approach also raises a scientific concern: Stem cells from arrested embryos might carry the risk of some undetected defect.

"If there was something wrong with the embryo that made it arrest, isn't there something wrong with these cells?" that could cause problems with their use, he asked. "We don't know."