title: Erratum.
abstract: In the first paragaph on page 1005 of the article "A molecular basis for MHC class II-associated autoimmunity" by John A. Todd et al. (20 May, p. 1003), invention of the polymerase chain reaction amplification method was incorrectly attributed to "Erlich and colleagues." The method was invented by Kary Mullis at the Cetus Corporation and developed by Erlich's group.