A recent development in the area of postconviction relief is the mitochondrial DNA (mtDNA) re-examination of shed crime-scene hairs that were previously examined using only a microscope. In the 1990s, mtDNA analysis was introduced for samples unsatisfactory for STR profiling. Nuclear DNA is present in only two copies per cell; however, the small circular mtDNA molecule is present in hundred to thousands of copies per cell. A limitation of mtDNA is its inheritance only from the mother, which means that all a woman's offspring, her siblings, her mother, and other maternal relatives will have the same mtDNA; it does not have the unique identifying capability of nuclear DNA. Still, in most cases in which a mtDNA match is obtained, it is possible to eliminate well over 99 percent of the general population as contributors of a specific hair, with the exception of maternal relatives. This article cautions, however, that by themselves, hairs are not indicative of any specific activity or time frame for the donor's presence at the crime scene. Exceptions to this are forcibly removed hairs under the victim's fingernails during a struggle, or pubic hairs, which are not shed onto floors or furniture as often as head hairs. This article describes the mtDNA analytical process, and two relevant case studies are briefly described. 5 figures and 3 suggestions for additional reading