The changes in physical and chemical characteristics derived from genetic alteration are the basis for the development of mutation assays. Among the ever-increasing number of mutation assays available, most are variants of allele-specific primer extension targeting single nucleotide polymorphism (SNP) and point mutations. Conventional allele-specific primer extension was designed to work using exo- polymerases exclusively, regardless that the fidelity of DNA polymerases has been recognized for more than three decades depending on the presence of proofreading activity provided by its internal 3 exonuclease. Recently, exo+ polymerase with proofreading activity has been applied in mutation detection. The application of proofreading activity by DNA polymerase with 3 to 5 exonuclease provides two significant advantages: elimination of false positives and applicability to both real-time PCR as well as microarray platforms. Technologically, the high fidelity DNA polymerases offer a variety of applications in genetic analyses, including mutation detection, high fidelity expression profiling, and de novo sequencing. Some of these applications can be immediately applied in pharmacogenetics studies, particularly in the filed of somatic Pharmacogenetics.