Nat. Biotechnol. 24, 397–400 (2006); published online 29 March 2006; corrected after print 8 November 2006.

In the version of this article initially published, on page 399, column 2, paragraph 4, the authors wrongly credited the idea for using cells from nonviable human embryos as an alternative source of human embryonic stem cells to Landry and Zucker (refs. 7,26). The reference should have been to Alikani, M. & Willadsen, S.M., Reproductive BioMedicine Online 5, 56–58, 2002.