Medical Sciences. In the article “t(11;22)(q23;q11.2) in acute myeloid leukemia of infant twins fuses MLL with hCDCrel, a cell division cycle gene in the genomic region of deletion in DiGeorge and velocardiofacial syndromes” by Maureen D. Megonigal, Eric F. Rappaport, Douglas H. Jones, Terrence M. Williams, Brian D. Lovett, Kara M. Kelly, Paul H. Lerou, Thomas Moulton, Marcia L. Budarf, and Carolyn A. Felix, which appeared in number 11, May 26, 1998, of Proc. Natl. Acad. Sci. USA (95, pp. 6413–6418), the authors wish to note the following corrections. On page 6414, column 2, line 4, the text should read: “The 24-μl ligation reaction mixture contained 0.5 μg” not “0.05 μg” as printed. Also, on page 6415, column 1, line 56, the text should read: “AmpliTaq DNA polymerase, all four dNTPs (each at 200 μM)” not “(each at 250 μM)” as printed.