Paraoxonase-1 (PON1) is a serum esterase associated with high density lipoproteins and capable of detoxifying toxic metabolites of organophosphorus (OP) compounds. Two major polymorphisms have been described in the coding region of the PON1 gene at positions 192 and 55 and at least five in the 5′-regulatory region, the most important at position -108. Depending on the substrate, PON1 192 Q/R polymorphism can affect PON1 enzymatic activity. In the present study, we have determined the distribution of the PON1 192 Q/R and -108 C/T polymorphisms in a Peruvian population and compared the distribution of these polymorphisms with those of other world populations. PON1 phenotype and enzyme activity also were measured as they can influence the population resistance to the toxicity of OP compounds. The genotype distribution at position 192 was: QQ = 0.236, QR = 0.607, and RR = 0.157; and distribution at position -108 was: CC = 0.315, CT = 0.596, and TT = 0.089. The frequencies of the high activity R and C alleles were 0.461 and 0.613, respectively. The frequency of the PON1 192 Q allele was significantly lower than that of American, Caucasian-American, European-Brazilian, and Costa Rican samples. Outside the American continent, the frequency of this allele was lower than for all European countries, Thais, and Indians, but higher than for Chinese or Japanese. Regarding the toxicological importance of these polymorphisms, it was inferred that PON1 phenotyping (assessment of the R alloform) and genotyping (determination of the PON1 -108TT genotype) could be helpful as individual markers of susceptibility. PON1 phenotyping may be useful in further epidemiological studies involving agriculture workers occupationally exposed to OP compounds in developing countries. © 2006 Wiley-Liss, Inc.