Few recent papers in biology have received as much praise as Woo Suk Hwang’s 2004 and 2005 announcements of cloning human embryonic stem cells – or fallen as fast into disrepute with the discovery that they were rank fakes. Embryonic stem cell (ESC) research is no less promising today than it was before Hwang’s deceit was revealed; most investigators continue to believe that it will eventually yield revolutionary medical treatments. The fact that no one has yet derived ESCs from cloned human embryos simply means that the science is less advanced than has been supposed over the past two years. Still, Hwang has badly undermined the reputation of a field that already has more than its share of political and public relations problems. Some longtime opponents of ESC research will undoubtedly argue that Hwang’s lies only prove that the investigators cannot be trusted to conduct their work ethically, and the public may believe them.