Cytological, cytochemical and molecular investigations have shown different trends in DNA evolution among different lineages of reptiles. In chelonians, qualitative and quantitative differences in all the main DNA fractions (highly repetitive, middle repetitive and single‐copy DNAs) have been found. These variations do not seem to be correlated with phylogeny nor with the taxonomic position of the species studied so far; they might result mainly from variations in the amount of non‐functional DNA fractions.