In the January 2017 issue, the piece “Living therapeutics: Scientists genetically modify bacteria to deliver drugs” (Nat. Med 23, 5–7, 2017) incorrectly stated that the company Oragenics is slated to launch a phase 2 trial on ulcerative mucositis next year. In fact, they will begin the trial in 2017. The error has been corrected in the HTML and PDF versions of this article.