Oxidative phosphorylation (OXPHOS) diseases are caused by inherited or spontaneously occurring mutations in the mitochondrial DNA (mtDNA) or the nuclear DNA. Mutations in the mtDNA can be classified into two groups, rearrangements and point mutations. This unit describes a method for detecting rearrangements of the mtDNA, which involves Southern blot hybridization. Another protocol detects mtDNA point mutations using restriction analysis of polymerase chain reaction (PCR) products. The Southern blot method requires an mtDNA-specific probe.