IMMUNOLOGY. For the article “Posttranscriptional regulation of Bruton's tyrosine kinase expression in antigen receptor-stimulated splenic B cells” by Sazuku Nisitani, Anne B. Satterthwaite, Koichi Akashi, Irving L. Weissman, Owen N. Witte, and Matthew I. Wahl, which appeared in number 6, March 14, 2000, of Proc. Natl. Acad. Sci. USA (97, 2737–2742), the authors note the following correction. In Materials and Methods, erythrocytes were lysed by incubation of cells in 0.15 M NH₄Cl, 10 mM KHCO₃ (not 0.1 M KCL as stated), and 0.1 mM EDTA (30, 31).