The paraoxonase or PON family of genes resides on human chromosome 7q2t-22 in the order PONt, PON3 and PON2. PONt was one of the early genes identified as an environmentally relevant gene, in that it is important in determining an individual's sensitivity or resistance to exposure from specific organophosphorus (OP) insecticides. Paraoxonase (PONt) is an A- esterase (i. e., not inhibited by OP compounds) initially identified for its ability to catalytically hydrolyze paraoxon, the toxic metabolite (oxon form) of the insecticide parathion. Evidence accumulated in the past several years has...