Biochemistry. In the article “Oxidative damage during aging targets mitochondrial aconitase” by Liang-Jun Yan, Rodney L. Levine, and Rajindar S. Sohal, which appeared in number 21, October 14, 1997, of Proc. Natl. Acad. Sci. USA (94, 11168–11172), the authors request that the following correction be noted. On page 11169, in the paragraph on enzyme activity assay, line 8, “isocitrate” should be “citrate.” The next sentence on method 2 should read: “Method 2 is based on the formation of both citrate and isocitrate from cis-aconitate … .” This same change applies to the description of the enzyme activity assay in the legend of Fig. 2A.