The purpose of this paper is to provide a brief review of the current state of our knowledge regarding pesticides and oxidative stress. To this end, we performed a search of the literature using Medline/Index Medicus, EMBASE/Excerpta Medica, and Chemical Abstracts; most of the relevant citations were studied and summarized. In order to better understand the nature of oxidative stress, the principles of free radical production and the body's normal defense system are discussed. The pesticides are categorized and discussed according to their ability to produce lipid peroxidation or alter body antioxidant status. It is concluded that stimulation of free radical production, induction of lipid peroxidation, and disturbance of the total antioxidant capability of the body are mechanisms of toxicity in most pesticides, including organophosphates, bipyridyl herbicides and organochlorines.