The physiological role of mammalian paraoxonase/arylesterase is unknown. However, paraoxonase is an HDL-associated protein, and recent studies indicate that it may have anti-atherogenic functions. We describe the chromosomal localization and structure of the mouse paraoxonase gene (Pon1) to establish Pon1 as a candidate gene for genetically determined traits or pathological states in the mouse. The coding portion of Pon1 extends over approximately 25-26 kb and consists of nine exons and eight introns. We also present nucleotide sequences from the 5'-flanking region of Pon1 containing numerous consensus sequences for DNA binding proteins. Haplotype analysis of 94 N2 progeny from an interspecific cross indicates that Pon1 is localized on proximal mouse chromosome 6 near D6Mit86. This assignment excludes Pon1 as a candidate for the atherosclerosis susceptibility genes Ath1, Ath2, and Ath3. However, Pon1 is a promising candidate for the remaining unmapped Ath genes.