Very recent investigations have provided evidence for a higher DNA methylation level in polar and sub-antarctic fishes compared to temperate/tropical fishes, the latter being in turn higher than the DNA methylation level of warm-blooded vertebrates. These results confirm and extend the finding [Jabbari, K., Cacciò, S., Pais de Barros, J.P., Desgres, J., Bernardi G., 1997. Evolutionary changes in CpG and methylation levels in the genome of vertebrates. Gene 205, 109-118] that DNA methylation level of vertebrates is inversely related to body temperature. Here we studied the methylation level of reptilian genomes. The species previously analyzed exhibited methylation levels closer to those of mammals and birds rather than to those of fishes and amphibians. The sample was, however, too small to reach a final conclusion. Here we used Reversed-Phase-High-Performance Liquid Chromatography (RP-HPLC) to analyze the DNA methylation levels of 43 reptiles representing three out of four orders and 20 families. Such analysis has shown that snakes and lizards exhibit methylation levels covering the whole range comprised between those of temperate/tropical fish and mammals, while turtles, and, more so, crocodiles are close to mammals. We discuss some ecological and physiological data that explain these results.