Nat. Biotechnol. 26, 1227–1233 (2008); published online 7 November 2008; corrected after print 9 February 2009

In the version of this article initially published, 2007 US sales of therapeutic enzymes in Figure 3 were incorrectly listed as $0.7 billion. They should be $0.9 billion. In the same figure, the 2007 growth (%) was incorrectly listed as −14%; it should be 18%. On page 1230, human growth hormone sales growth rate was incorrectly reported as 45%; it should be 5%. The errors have been corrected in the PDF and HTML versions of this article.