For the first time, researchers have created embryonic stem cells using the same cloning techniques that made Dolly the sheep.
Researchers at the New York Stem Cell Foundation laboratory took adult skin cells and merged them with an unfertilized human egg.
They then triggered the egg to develop and were able to extract embryonic stem cells.
Until now, they had never been able to get the egg to grow.
In this new experiment they did not completely replace the egg's DNA with the skin cell DNA, and that seemed to be the trick.
Embryonic stem cells can be molded into any cell type in the body.
Researchers say this could help them treat conditions like diabetes and heart disease, because they can replace damaged cells with new ones.
The new cells would not be rejected by the donor's immune system, because their own skin cells were used in the process.
Outside experts say there are still several hurdles to overcome before these cells can be used in clinical practice.