consent form. All participants were asked questions on their work history. 10mL blood samples were then taken from an arm vein using disposable needles and syringes and transferred to test tubes. After clotting, serum was separated by centrifugation, transferred to a Teflon stoppered sample vial and kept under ice for transportation to the laboratory of the Federal University of Mato Grosso, where the samples were immediately frozen. DDT residues were analyzed using the method previously described by Minelli & Ribeiro (1996b), which consists of pesticide extraction from a serum-silica suspension with n-hexane-acetone (9:1), extract purification using alumina column chromatography, and analysis of the final extract using gas-liquid chromatography with electron capture detection (63Ni). All solvents were residue grade, and reference standards were 98-99% pure, purchased from Supelco. Standard solutions were prepared in isooctane. All samples were analyzed in duplicate, and the results were presented as a mean of the two results. Chromatographic parameters were as follows: carrier gas: high purity nitrogen; gas flow: 30mL/min; oven temperature: 200oC; injector temperature: 235oC; detector temperature: 300oC; glass column (1,8m x 2mm i.d.) packed with 1.5% OV-17 + 1,95% QF-1 on 80-100 mesh Chromosorb WAW DMCS. Limits for residue quantification were determined as: p,p'DDT = 7.5 g/L and p,p'DDE = 5 g/L. Results and discussion Serum p,p'DDE, p,p'DDT, and total DDT concentrations as well as the age, work duration, and jobs of volunteers from the District of Sinop are shown in Table 1. p,p'DDE was detected in 98% of the samples, while p,p'DDT was found in 85.7% (36 samples). Dechlorination of p,p'DDT in the human body results in p,p'DDE, which is more persistent than the parent compound, and DDE expressed as a percentage of total DDT increases after DDT intake decreases (WHO, 1979). Sprayers and drivers had not been exposed to DDT since 1997, which explains the fact that p,p'DDE levels were much higher than those of p,p'DDT in almost all of the samples. Study subject number 38 presented pesticide concentrations much higher than the other unexposed workers, because he also worked as a storekeeper, where he handled DDT. This result was thus excluded from the unexposed sub-sample for statistical calculations. Table 2 shows the serum p,p'DDE, p,p'DDT, and total DDT concentrations, age, work duration, and jobs of blood sample donors from the District of Caceres. Similar to the results in Sinop, p,p'DDE was detected in all samples, while p,p'DDT was found in only 16 samples (48%). According to the Kolmogorov-Smirnoff normality test, these results are not statistically normal. The descriptive statistical data for p,p'DDE, p,p'DDT, and total DDT levels are presented in Table 3, for sprayers, drivers, and unexposed workers. The comparison of these concentrations for exposed individuals (sprayers and drivers) and unexposed workers in the District of Sinop using the Mann-Whitney non-parametric variance analysis showed that there is a significant difference (p <> 0.05). This indicates that despite their job differences, sprayers and drivers had been equally exposed. The same trend was observed in the District of Caceres. No correlations were found between serum pesticide levels and age or work duration in the study