Studies have reported a large interindividual variation in susceptibility to health effects caused by exposure to xenobiotic compounds such as drugs or chemical carcinogens. There is evidence that this can be partly explained by the existence of genetic polymorphisms in metabolic enzymes, such as cytochrome P450 (CYP450), N -acetyltransferases (NATs), and glutathione S -transferases (GSTM, GSTT, GSTP) [see, e.g., Refs. (1)(2)(3)(4)]. However, studies investigating associations between genetic polymorphisms and disease have reported conflicting results, probably caused by insufficient statistical power (5). Moreover, the majority of these studies focused on single polymorphisms. Regarding the number of genes implicated in the metabolism of xenobiotics and the large number of polymorphisms present in the human genome (6), these approaches fail to fully determine the role of genetic variation in an individual’s susceptibility to xenobiotic exposures. Such observations underline the need for methodologies that allow for high-throughput, low-cost genotyping of multiple polymorphisms in large populations (7)(8). In this study we describe the development, validation, and application of a cost-effective and rapid method for simultaneous genotyping of nine polymorphisms in five key enzymes involved in metabolism of xenobiotics: CYP1A2, GSTM1, GSTP1, GSTT1, and NAT2. The fragments containing the nine single-nucleotide polymorphisms (SNPs) were amplified in one sevenplex and one duplex PCR reaction (Table 1⇓ ). Primers were obtained from Qiagen. For the sevenplex PCR, a 50-μL reaction mixture was prepared containing PCR buffer, 0.2 mM deoxynucleotide triphosphates, 0.5 mM MgCl2, 1.25 U of Platinum® Taq Polymerase (Invitrogen), and 200 ng of template DNA. The final primer concentrations were 0.22 μM (for GSTP1 * 3 , GSTT1 , NAT2 * 6 , and NAT2 * 7 ), 0.45 μM (for CYP1A2 * 1F and NAT2 * 5 ), and 0.16 μM (for GSTP1 * 2 ). PCR was …