Neurobiology. In the article “Elevated free nitrotyrosine levels, but not protein-bound nitrotyrosine or hydroxyl radicals, throughout amyotrophic lateral sclerosis (ALS)-like disease implicate tyrosine nitration as an aberrant in vivo property of one familial ALS-linked superoxide dismutase 1 mutant” by L. I. Bruijn, M. F. Beal, M. W. Becher, J. B. Schulz, P. C. Wong, D. L. Price, and D. W. Cleveland, which appeared in number 14, July 8, 1997, of Proc. Natl. Acad. Sci. USA (94, 7606–7611), the following correction should be noted. The citation to the work of Samuel M. Chou and Helen S. L. Wang (ref. 48) in the above paper was incorrectly attributed to J. Neuroanat. It should have been J. Chem. Neuroanat.