Since the publication of the second edition of Free Radicals in Biology and Medicine in 1989 the techniques of modern molecular, cellular, and structural biology have provided new data that have transformed scientific thinking about topics within free radical research. New reactive species, such as peroxynitrite, have been discovered to have a role in biological systems. Therefore much of the third edition has been completely rewritten and what remains from the second has been thoroughly updated. There are new chapters on antioxidant defence systems in bacteria, plants, and animals; the detection of free radicals; the role of antioxidants in ageing, nutrition, disease, and therapy; and a new appendix on molecular biology. The chapter on oxidative stress and its consequences includes the damage and repair of DNA, proteins, and lipids, cytokines, and cell death (both apoptosis and necrosis). Free radicals and other reactive species are now implicated in a wide range and number of diseases and the third edition covers their role in hypertension, diabetes, lung damage, cystic fibrosis, nervous system disorders, viral infections, and cancer. The toxicology chapter has been updated to include new sections on complex mixtures, nitro- and azo- compounds, and radiation. Erythrocytes, chloroplasts, the eye, the skin, reproduction, and exercise are covered as special cases of oxidative stress and antioxidant protection. Reactive species can act as useful biomolecules and this role is fully discussed. There is also an up-to-date introduction to free radical chemistry (as well as a basic chemistry appendix) and oxygen toxicity. Each major statement in the text is referenced. The authors have maintained the simplicity of approach and readability of the previous editions to make this book an invaluable companion to all those interested in the role of free radicals in life.