1. The genetically polymorphic cytochrome P450 enzymes 2C9 (CYP2C9) and 2C19 (CYP2C19) are involved in the metabolism and elimination of a number of widely used drugs. The polymorphisms give rise to substantial interindividual and interethnic variability in drug excretion rates and final serum concentrations. For this reason, therapeutic responses and adverse drug reactions may vary from one person to another. In the present study we determined CYP2C9 and CYP2C19 genotypes in a random Iranian population to compare allele frequencies with previous findings in other ethnic groups. 2. Allelic variants of CYP2C9 (*1/*2/*3) and CYP2C19 (*1/*2/*3) were determined in 200 unrelated healthy Iranian volunteers by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assays. 3. Fifteen subjects (7.5%) were homozygous for the CYP2C9*2 allele, whereas 21 individuals (10.5%) were heterozygous for this allele and 164 subjects (82%) had the wild-type allele (CYP2C9*1). No CYP2C9*3 was detected in the population sampled. Six subjects (3%) were homozygous for CYP2C19*2, whereas 44 individuals (22%) were heterozygous for this allele. In the remaining subjects (75%), no CYP2C19*2 was found. In addition, no CYP2C19*3 was detected in the population sampled. 4. Based on our data, the frequency of the CYP2C9*2 allelic variant in Iranians is similar to that in other Caucasian populations; however, the frequency of the CYP2C9*3 allele differed significantly (P < 0.05). Conversely, there was no difference in the frequency of CYP2C19 allelic variants between the present study and other studies evaluating this allele in Caucasian populations (P > 0.05).