Background: Cytochrome P450 2C19 (CYP2C19) is a polymorphically expressed enzyme that shows marked interindividual and interethnic variation. CYP2C19*2 and CYP2C19*3 are the most frequently identified defective alleles in Orientals and Caucasian poor metabolizers (PM). The aim of this study was to investigate the frequencies of CYP2C19*1, CYP2C19*2 and CYP2C19*3 alleles and CYP2C19 genotypes in the Mazandarani ethnic group among Iranian Population. 
Materials and Methods: The study was conducted in 103 unrelated healthy volunteers. DNA was extracted from leucocytes and analyzed by the PCR-RFLP protocol. The PCR product was digested with restriction enzymes (SmaI and BamH1) and then separated electrophoretically using polyacrylamide gel..
Results: Of the alleles tested, CYP2C19*1, and CYP2C19*2, but not CYP2C19*3, were detected. The frequencies for CYP2C19 alleles *1, *2, and *3 were 91%, 9.0%, and 0.0%, respectively. The frequencies of CYP2C19 genotypes *1/*1, *1/*2, *1/*3, *2/*2, *2/*3 and *3/*3 were 84%, 14%, 0.0%, 2.0%, and 0.0%, respectively.
Conclusion: The result of the present study showed that the two inactive alleles of CYP2C19 accounted for 9.0% of CYP2C19 alleles in our sample versus 8.8 - 40.1% reported in other populations. The frequencies of the studied alleles resulted significant differences between our sample and African and Eastern Asian populations.