ABSTRACT. Resistance to metronidazole (Mtz) in Helicobacter pylori is a major problem worldwide, especially in developing countries. Alterations in Mtz nitroreductase enzymes, such as oxygen-insensitive NADPH nitroreductase (RdxA) and NADPH flavin oxidoreductase (FrxA), are the major contributing factors for this resistance. In this study, rdxA and frxA were amplified, sequenced, and analyzed in 34 Mtz-resistant H. pylori isolates (MIC ≥ 8 µg/mL) using multiple allelespecific polymerase chain reaction (MAS-PCR); this method was developed to target the most common genotypes of rdxA in H. pylori. In this study, the rdxA and frxA genes in Mtz-resistant H. pylori strains displayed a large number of point mutations. The rdxA and frxA genes of Mtz-resistant clinical isolates showed a higher percentage of missense mutations (97.1 and 78.6%, respectively) compared to 26695 reference strains; additionally, missense mutations were more common than frameshift (20.6 and 32.1%) and nonsense mutations (8.8 and 10.7%, respectively) in these genes. The most common missense mutations in rdxA were D 59 N (94.1%), T 31 E (88.2%), and R 131 K (85.3%). The most common missense mutations in frxA were F 72 S (57.1%), G 73 S (57.1%), and C 193 S (53.6%). The developed MAS primers, specific to position 175 and 392 of rdxA, successfully amplified the common alleles and distinguished the variants. MAS-PCR could be a useful tool for epidemiological studies of H. pylori, associated with Mtz resistance. rdxA variants must be screened in order to ensure the effectiveness of Mtz-based H. pylori therapies in developing countries.