Immunology. In the article “Parasite-mediated nuclear factor κB regulation in lymphoproliferation caused by Theileria parva infection” by Guy H. Palmer, Joel Machado, Jr., Paula Fernandez, Volker Heussler, Therese Perinat, and Dirk A. E. Dobbelaere, which appeared in number 23, November 11, 1997, of Proc. Natl. Acad. Sci. USA (94, 12527–12532), the following correction should be noted. The concentration of N-acetylcysteine used in the experiments was 30 mM, not 25 μg/ml as erroneously reported on page 12528, lines 14 and 15 of the paragraph entitled “Cell Lines and Cultures” in the Materials and Methods section.