CYP2D6 is polymorphically expressed enzyme that show marked interindividual and interethnic variation. Phenotyping of CYP2D6 provides valuable information about real-time activity of this important drug-metabolizing enzymes through the use of specific probe drugs. The aim of this study was to identify the CYP2D6 oxidation phenotype with dextromethorphan (DEX) as a probe drug in Mazandarani ethnic group among Iranian population.The study included 71 unrelated healthy volunteers. Dextromethorphan hydrobromide (30 mg) was given orally to healthy subjects and peripheral venous blood samples (10 ml) were taken at 3 hr post-dose. Dextromethorphan and the metabolite dextrorphan (DOR) were analyzed by the HPLC method. The log DEX/DOR metabolic ratio (MR) at 3 hr plasma sample was used as the index of CYP2D6 activity and a value of 0.3 was used as the antimode separating extensive metabolizers (EM) and poor metabolizers (PM) phenotypes.A 560-fold interindividual variation in dextromethorphan MRs was observed in this study. Considering the antimode 0.3 in log scale, 7.04% (5/71) volunteers were identified as PMs. Conclusion : The result showed that the frequency of CYP2D6 PM phenotypes accounted for 7.04% of subjects in our samples. Despite these findings, we propose a further study in larger samples to provide a wider image and to get more valuable information upon pharmacogenetic basis for individual therapy and personalized medicine.