Free radicals are highly toxic compounds which can react with a number of molecules such as glycoproteins or amino acids. These reactions can lead to the denaturation of proteins, destabilization of cellular membrane and eventually, cell death. Free radicals have been recently implicated in the pathogenesis and clinical course of a number of neuropsychiatric disorders including aging of the central nervous system (CNS), schizophrenia, and the development of tardive dyskinesia during chronic use of neuroleptics. This paper provides an overview of the nature of free radicals and discusses briefly their participation in the toxicity associated with catecholamines in the CNS.