Cytochrome P450 3A5 (CYP3A5) is involved in the biotransformation of many orally administered drugs, some of which are dose optimized using therapeutic drug monitoring. The CYP3A5 gene exhibits variable inter-individual expression, which is related to a single-nucleotide polymorphism. Producers of the enzyme possess at least one CYP3A5*1 allele. Knowledge of patients' CYP3A5 genotype, in conjunction with therapeutic drug monitoring (TDM), may aid patient management. Real-time polymerase chain reaction (PCR) was used to genotype the A6986G mutation of the CYP3A5 gene. Specific primers were employed to generate a DNA product, co-amplified with two internal hybridization probes, using a LightCycler. DNA melt curve analysis readily identified the genotypes CYP3A5*1/*1, CYP3A5*1/*3 and CYP3A5*3/*3. Results were confirmed using DNA sequencing with 100% correlation. Genotypes were determined from 263 individuals and compared with the genotypes of a pseudogene CYP3AP1, which is in disequilibrium with CYP3A5. This is a rapid and reliable method for genotyping the CYP3A5 polymorphism which may be used as an important adjunct to the TDM service offered by laboratories to optimize drug prescription.