Recent pharmacogenomic studies have revealed significant interethnic differences in glutathione S-transferase (GST) allelic frequencies among various ethnic groups. Therefore, we have investigated <i>GSTM1</i> (gene deletion), <i>GSTT1 </i>(gene deletion) and <i>GSTP1</i> (rs1695) polymorphism frequencies in 3 Brazilian ethnic groups (n = 203). <i>GSTM1 </i>and <i>GSTT1 </i>polymorphism analyses were performed by multiplex polymerase chain reaction, and <i>GSTP1</i> (rs1695) analysis was done by polymerase chain reaction restriction fragment length polymorphism. <i>GSTM1–</i> polymorphism frequency was 33.2%, while <i>GSTT1</i> null <i>(GSTT1–)</i> was 30.2%. The valine <i>GSTP1*B</i> (rs1695) allele was present in 35.1% subjects, while the heterozygous form (isoleucine/valine) was the most prevalent genotype (46.6%). We found a statistically significant difference in genotype frequency among Amerindians versus Caucasians (p = 0.016) and among Amerindians versus African-Americans (p = 0.033). Considerable frequency variation was found in our study, even when compared with other studies showing phylogeographical heterogeneity to the genes studied in Brazilian populations.