Scientists for the first time have turned ordinary skin cells into what appear to be embryonic stem cells - without having to use human eggs or make new human embryos in the process, as has previously always been required, a Harvard research team announced Sunday.

The new technique uses laboratory grown human embryonic stem cells, such as the ones President Bush has approved for use by federally funded researchers, to "reprogram" the genes in a person's skin cell, turning that skin cell into an embryonic stem cell itself.

Moreover, since the new stem cells made this way are essentially rejuvenated versions of a person's own skin cells, the DNA in those new stem cells matches the DNA of the person who provided the skin cells. In theory at least, that means that any tissues grown from those newly minted stem cells could be transplanted into the person to treat a disease without much risk that they would be rejected, since they would constitute an exact genetic match.

Until now, the only way to turn a person's ordinary cell into a "personalized" stem cell such as this was to turn that ordinary cell into an embryo first and later destroy the embryo to retrieve the new stem cells growing inside, a process widely known as "therapeutic cloning."

That prospect, like others in the promising arena of human embryonic stem-cell research, has stirred strong emotions among those who believe that days-old human embryos should not be intentionally destroyed.