Medical Sciences. In the article “Cancer-specific chromosome alterations in the constitutive fragile region FRA3B” by Koshi Mimori, Teresa Druck, Hiroshi Inoue, Hansjuerg Alder, Lori Berk, Masaki Mori, Kay Huebner, and Carlo M. Croce, which appeared in number 13, June 22, 1999, of Proc. Natl. Acad. Sci. USA 96, 7456–7461, the following correction should be noted. FHIT exon 4 was misplaced in Figs. 1 and 2. Its true placement is ≈40 kilobase pairs further centromeric at base pairs 162581 to 162673 of GenBank submission AF152363. Thus, the length of intron 4 is 284935 base pairs and the markers D3S4489 and D3S4260 and the proximal aphidicolin-induced hybrid breaks are telomeric to exon 4, i.e., in intron 4.