Nat. Biotechnol. 33, 228–231 (2015); published online 6 March 2015; corrected after print 12 October 2016

In the version of this article initially published, on p.231, left-hand column, the maker of linaclotide was said to be Redwood rather than Ironwood Pharmaceuticals. In addition, linaclotide is no longer referred to as a “homolog of the enterotoxin peptides,” but as “similar to the enterotoxin peptides,” and it has been clarified to be “rationally designed.” The errors have been corrected in the HTML and PDF versions of the article.