total HCH and 8.55 9.14g/L for total DDT. In this group, o,p'DDT and p,p'DDD were not detected and p,p'DDT was found in only three samples, while p,p'DDE appeared in all samples, with a mean concentration of 8.32 9.03g/L. Among the three exposed groups that were studied (one group with recent but not past exposure to DDT, one with past but not recent exposure, and one with both past and recent exposure), the latter showed the highest mean serum concentration, with 732.50 685.20g/L. From the occupational health point of view, all exposed groups presented total serum DDT levels above the values considered normal in NR-7 (see below), that is, 30g/L. Act 6,514 (Dec. 22, 1977) of the Brazilian Ministry of Labor, in its Regulatory Provision NR-7, established threshold limit values (TLVs) for chemicals in biological samples from workers. TLVs are the maximum tolerable concentrations of endogenous substances not to be exceeded in the human body. For serum DDT, the TLV was set at 500g/L. According to this same legislation, normal serum DDT concentration in individuals without occupational exposure to this chemical was 30g/L. These guidelines were re-edited in 1994, when organochlorine pesticides were excluded. Minelli & Ribeiro (1996a) determined serum insecticide residues in 26 sprayers who had handled HCH and DDT in malaria vector control campaigns in Sao Jose do Rio Preto, Sao Paulo State. The control group of unexposed workers consisted of 16 individuals. The substances o,p'DDT and g-HCH were detected in 62% and 92% of the samples, respectively. All blood samples were contaminated with a-HCH, b-HCH, p,p'DDT, and p,p'DDE at mean concentrations of 0.4, 31.8, 64.3, and 13.5g/L, respectively. The levels of b-HCH, p,p'DDE, and p,p'DDT were considerably higher than those found in samples of unexposed workers, with mean concentrations of 3.3, 14.3, and 1.5g/L, respectively Recent studies of groups not occupationally exposed to organochlorine pesticides were conducted in Brazil by Koifman et al. (1998), Paumgartten et al. (1998), and Delgado et al. (2002). The first group performed a case study to investigate the occurrence of a cancer cluster among young indigenous adults in an Amazonian village. The authors evaluated the different environmental exposures possibly associated with this cancer cluster, i.e., exposure to ionizing radiation, organochlorine (DDT) and organophosphorus pesticides, and heavy metals. 89 blood samples were analyzed, and median serum p,p'DDT ranged from 26.3g/L (men 30 years of age or older) to 58.1g/L (children). Serum organochlorine pesticide levels were determined in agricultural workers from Rio de Janeiro State by Paumgarten et al. (1998). p,p'DDE was detected in 16 of 26 samples, but p,p'DDE exceeded the limit of quantification of 1.4 g/L in only three samples. Delgado et al. (2002) analyzed organochlorine pesticides in blood samples from 33 volunteers who had been living in Greater Metropolitan Rio de Janeiro for at least 5 years. p,p'DDE was found in 17 of the 33 samples at levels varying from 1.4 to 4.8g/L. Organochlorines are known to be toxic to the central and peripheral nervous systems, causing hypersensitivity in nerves and muscles (WHO, 1979). There is still controversy over the adverse effects of chronic