The primary objective of this study is to establish the role of dopamine in the peroxynitrite mediated toxicity of Methamphetamine. Methamphetamine is a drug of abuse whose prevalence is increasing worldwide especially among the young. The high rate of abuse and the potential for neurotoxicity are compelling reasons for elucidating the mechanism of methamphetamine's actions. Recently, much attention has been given to the role of oxidative stress in the mechanism of methamphetamine's action. Recently, much attention has been given to the role of oxidative stress in the mechanism of methamphetamine toxicity. Nitric oxide and superoxide, in particular, have been implicated in this process. The diffusion limited reaction of nitric oxide and superoxide yields peroxynitrite, a powerful reactive species capable of protein modification and oxidizing lipid membranes. Dopamine, an obligatory factor in Methamphetamine toxicity, is elevated in the cytoplasm and is able to react with peroxynitrite to form a dopamine- quinone. Dopamine-quinone is also highly toxic to cells by its ability to react with protein sulfhydryls and damage mitochondria. Deciphering the relationship between peroxynitrite and dopamine will further understanding about key mechanistic steps in methamphetamine toxicity. The techniques employed will include molecular biology, biochemical pharmacology, immunoprecipitation, cell culture, SDS-PAGE, western blotting, high performance liquid chromatography, spectrophotometric enzyme assays and enzyme activity assays.