Certain OPs, such as the oxygen analogs of commonly used insecticides (chlorpyrifos oxon, diazoxon, paraoxon) and nerve agents, such as sarin or soman, can be hydrolyzed by paraoxonase (PON1) [7]. The PON1 gene presents several polymorphisms in the coding and promoter regions that affect the catalytic efficiency of the enzyme toward different substrates (the Q192R polymorphism) and its level of expression (e.g., the C-108T polymorphism) [46] and [47]. Extensive research in transgenic animal models clearly indicates that PON1 “status”, encompassing both the Q192R polymorphism and the level of PON activity, plays a most relevant role in modulating the acute toxicity of some, but not all OPs [48] and [49]. The important determinant is the catalytic efficiency of each PON1 allozyme toward a specific substrate; thus, in case of chlorpyrifos oxon, PON1 provides protection in vivo, and PON1R192 provides better protection than PON1Q192; in case of diazoxon, both alloforms provide the same degree of protection, while in case of paraoxon, the substrate after which the enzyme was named, PON1 does not provide any protection due to an overall low catalytic efficiency of PON1 toward this substrate [48] and [49] ( Table 2). These studies in transgenic mice provide a convincing case of extrapolating the results obtained in animals to humans; however, direct and conclusive confirmation of the relevance of PON1 status in determining relative susceptibility to OP toxicity is still lacking [50] and [51]. This too is expected to be a fruitful area of future research.