In the February 2011 issue, the article entitled “Genzyme, though unique, could be a bellwether for US biotech” (Nat. Med. 17, 145, 2011) incorrectly stated that GlaxoSmithKline had acquired AstraZeneca. Although GlaxoSmithKline has acquired medicines from AstraZeneca in the past, the two companies never merged. The error has been corrected in the HTML and PDF versions of the article.