Peroxynitrite chemistry, a century-old area of research, has experienced a renaissance with the annual number of publications on the subject increasing from only one in 1990 to nearly 200 in 1998–2000. This renewed interest was stimulated by the discovery of the biological roles of nitric oxide, distinguished by the 1998 Nobel prize, and the recognition that the conversion of nitric oxide into peroxynitrite may play a major role in human diseases associated with oxidative stress and in cellular defense against invading pathogens.