The role of mitochondrial DNA (mtDNA) deletions in aging and in neurodegenerative diseases is often determined by measuring the amount of deleted mtDNA in the affected tissue. Upon examining brain autopsy tissue from a 59 year old individual with lung cancer we determined by serial dilution PCR and kinetic PCR that a greater ratio of deleted mtDNA was present in the caudate than in the parietal cortex. However, the magnitude difference for these two brain regions appeared to be technique dependent; by serial dilution PCR the caudate had 10 times more deleted mtDNA than the parietal cortex (0.0141 vs 0.0014) whereas kinetic PCR yielded a 4-fold difference (0.1258 vs 0.0316). These results indicate that although it is valid to compare the amount of deleted mtDNA in normal and diseased tissue and draw conclusions based on relative comparisons within one study, greater caution should be exercised when comparing absolute values from studies using different measurement techniques.