Human serum paraoxonase (PON1) is associated with high density lipoprotein (HDL) particles. This enzyme is involved in the metabolism of oxidized lipids and also plays a major role in the metabolism and detoxication of insecticides processed through the cytochrome P450/PON1 pathway. An Arg/Gln (R/Q) substitution at position 192 determines a substrate dependent activity polymorphism. In addition to the effect of the amino acid substitution on rates of hydrolysis of different substrates, there is a large interindividual variability in the amount of PON1 protein in sera that is stable over time. Recently, a number of reports based solely on PON1 genotyping have suggested that in some populations, the PON(R192) allele may be a risk factor for coronary artery disease. Another report notes an increased risk of the PON(R192) allele for Parkinson's disease. We report here the development of a two-dimensional, microtitre plate reader-based enzyme analysis that provides a high-throughput assessment of PON1 status. Population distribution plots of diazoxonase versus paraoxonase activities provides PON1 phenotype and an accurate inference of PON1 genotype. Both are important parameters for determining an individual's PON1 status. The analysis also provides PON1 allele frequencies for specific populations.