This chapter presents the subjects as in the second edition, updated with the latest results on the toxicokinetics of VX, mainly obtained after improvement of the analytical methodology. Toxicokinetic studies, together with toxicodynamic studies of nerve agents, provide a quantitative basis for the design of new strategies against intoxication with nerve agents. The interpretation and understanding of the toxicokinetics of nerve agents would not be possible without taking into consideration that these agents consist of mixtures of stereo-isomers, which are often extremely different in their toxicokinetic and toxicodynamic properties. Toxicokinetic studies are only interesting if the agents can be determined at levels that are toxicologically relevant. Toxicokinetic studies can be an adequate tool for the quantitative description of the protective mechanism, which is needed for registration of the enzyme as a pretreatment drug for application in humans. The toxicokinetics of soman in anesthetized, atropinized, and artificially ventilated naive and human butyrylcholinesterase-pretreated guinea pigs were studied.