Nat. Biotechnol. 27, 275–280 (2009); published online 1 March 2009; corrected after print 16 March 2009

In the version of this article initially published, the unit (nM) for the amount of TGF-b inhibitor (Tocris) reported in the Methods section “Neural induction” was incorrect. The correct unit is μM. The error has been corrected in the HTML and PDF versions of the article.