(PNASH Pilot 2000-2001) Compelling evidence from whole-animal and tissue culture studies indicate that pesticides, especially organophosphate pesticides (OP), induce oxidative stress. While the cholinergic properties of OPs are well-established, our understanding of their oxidative stress properties (especially on humans) is limited. Given the importance of oxidative stress in disease and the widespread use of pesticides, this project studied the relationship between OP pesticides and stress in humans by analyzing oxidative stress biomarkers in urine and lymphocytes of pesticide mixer/applicators. Work histories and information on current work practices was obtained. Dialkylphosphate metabolites, and work histories were used to estimate the internal dose and the levels of exposure. The project focused on the problem of chemical exposure in the agricultural work environment and how biomarkers can be used to assess the possible health hazards associated with chronic exposure to agrochemicals.