Mitochondrial respiratory chain disorders are clinically and genetically heterogeneous. There are several mitochondrial DNA (mtDNA) point mutations responsible for common mitochondrial diseases such as mitochondrial encephalopathy, lactic acidosis, stroke-like events, myoclonic epilepsy and ragged red fibers, neuropathy, ataxia, retinitis pigmentosa, and Leber's hereditary optic neuropathy. As a result of the clinical overlap, it is usually necessary to analyze more than one mutation for a patient suspected of a mitochondrial disorder. Molecular diagnosis is often performed using polymerase chain reaction (PCR)/restriction fragment length polymorphism (RFLP) analysis of the most likely point mutations. However, this method is time-consuming and often produces problems associated with incomplete restriction enzyme digestion. In addition, PCR/RFLP analysis may not be able to detect a low percentage of heteroplasmy. For a more effective method of diagnosing mtDNA disorders, we have developed a multiplex PCR/ allele-specific oligonucleotide (ASO) dot blot hybridization method to simultaneously analyze 11 point mutations. The PCR products from a DNA sample containing a homoplasmic wild-type or mutant mtDNA sequence will hybridize to either the wild-type or the mutant ASO probe. The PCR products of a heteroplasmic DNA sample will hybridize to both wild-type and mutant ASO probes. This PCR/ASO method allows the detection of low percentage mutant heteroplasmy.