This technique's advantage over nuclear DNA typing methods is the high copy number of mtDNA over nuclear DNA and hence the added sensitivity in cases involving a limited amount of DNA or significantly degraded DNA. The maternal inheritance of mtDNA offers the forensic scientist reference samples from maternally related individuals that are, barring mutations, identical, whereas nuclear DNA markers from related individuals share common alleles but are not genotypically identical. In performing this analysis, the replication of sequencing runs is a good way of overcoming sequence ambiguities. Laboratories should share templates, because many different methods exist for sequencing. Validation studies should be confined to examining the direct influence of common environmental agents such as dyes and bleaches on human hairs. Statistical interpretation of mtDNA sequence information is straightforward. Basic guidelines to facilitate the widespread use of the technique include the adoption of a common nomenclature, the amplification of extracts in duplicate whenever possible, sequencing in duplication, sharing of templates, and compilation of a human mtDNA database. Figures and 26 references