PHYSIOLOGY. For the article “Defining thyrotropin-dependent and -independent steps of thyroid hormone synthesis by using thyrotropin receptor-null mice,” by R. C. Marians, L. Ng, H. C. Blair, P. Unger, P. N. Graves, and T. F. Davies, which appeared in issue 24, November 26, 2002, of Proc. Natl. Acad. Sci. USA (99, 15776–15781; first published November 13, 2002; 10.1073/pnas.242322099), the authors note that due to an inadvertent duplication made during the assembly of Fig. 7A, lanes 4–6 (wtR, hR, and koR) are identical to lanes 1–3 (wt, h, and ko). The corrected figure and its legend appear below. This correction does not affect the conclusions of this article.