Nat. Biotechnol. 25, 1256–1264 (2007); published online 7 November 2007; corrected after print 7 December 2007

In the version of this article initially published, on p. 1258, paragraph 2, the incorrect serum concentrations to reach steady state and the incorrect accumulation ratio (Racc) for eculizumab were given. The corrected sentence reads “Eculizumab serum concentrations appear to reach steady state after 57 days. At steady state, the eculizumab accumulation ratio (Racc) was calculated to be 1.075.” In addition, in Figure 5, in the PDF version only, the word “assessment” was cut off the bottom of the box beginning “September 2006.” The final sentence should read “BLA and MAA submitted to FDA and EMEA, respectively; receive accelerated assessment.” And in Table 1, the heading “Units of packed RBCs transfused/patient/month” now appears in a separate row. The errors have been corrected in the HTML and PDF versions of the article.