In recent years a number of mitochondrial DNA (mtDNA) deletions have been detected in various tissues from individuals over 20 years of age. It has been postulated that these deletions are associated with natural aging. In order to determine whether a correlation exists between age and the amount of deleted 4977 bp mtDNA, we used two PCR reactions to study total DNA (nuclear and mitochondrial DNA) extracted from skeletal muscle (m. iliopsoas) obtained at autopsy from 93 individuals representing a wide age spectrum (range: 3 months-97 years). The primer pair L15/H15 was used to amplify a 533 bp fragment of intact mtDNA to determine the percentage of total DNA. A second PCR with the primer pair L35/H35 was then employed to amplify a 667 bp fragment of the deleted mtDNA. The amount of template DNA necessary to amplify the specific fragments of deleted mtDNA was found to decrease with age. Whereas no 4977 bp deletion could be detected in subjects under 20 years of age even with 1000 ng of total DNA, in individuals aged 21 to 30 years 1000 ng total DNA were sufficient. Only 1 ng total DNA was needed in all individuals over 70. Our results show that the 4977 bp deletion can be a useful marker of natural aging in human subjects.