[To check out a six-minute video featuring two eminent researchers and Technology Review's editor in chief discussing the hows and whys of embryonic stem-cell research -- with spectacular color graphics and images -- click here. Note: You can pause the video at any time.]

In late 2003, researchers at Advanced Cell Technology, a small biotech startup in Worcester, MA, thought they were about to do something remarkable. They had painstakingly generated cloned human embryos from adult cells and were trying to keep them alive long enough to harvest their inner cell masses, precious balls of cells that give rise to stem cells.