The mitochondrial DNA (mtDNA) was quantified by RT-PCR in skeletal muscle of the 3.5 month old mice. The skeletal muscle of 3.5 months old mice was chosen for quantification because, the thymidine phosphorylating activity was highest in the skeletal muscle and the Dm-dNK enzyme was active till 3.5 months of age. The results indicate that, there is no significant difference in the mtDNA copy number in the wild-type and the Dm-dNK^+/- positive mice.