Pharmacology. The article “Nonsteroid drug selectives for cyclo-oxygenase-1 rather than cyclo-oxygenase-2 are associated with human gastrointestinal toxicity: A full in vitro analysis” by Timothy D. Warner, Francesco Giuliano, Ivana Vojnovic, Antoaneta Bukasa, Jane A. Mitchell, and John R. Vane, which appeared in number 13, June 22, 1999, of Proc. Natl. Acad. Sci. USA (96, 7563–7568), contained an error in the compound DFP, which is incorrectly listed as diisopropylfluorophosphate. The correct compound is 3-(2-propyloxy)-4-(4-methylsulphonylphenyl)-5,5-dimethylfuranone.