Amphibians have proved to be especially useful for monitoring environm
ental conditions: in fact, during their life cycle they alternate a do
uble array of morpho-functional characters which make larvae fit for f
reshwater environments and adults fit for the terrestrial ones. The lo
w vagility of amphibian populations and the development of adaptive st
rategies more similar to those of invertebrates than to those of tetra
pods, allow the exploitation of these organisms as sensitive bioindica
tors of the environmental conditions; however these same characters ap
pear to expose them to a decline that, in the opinion of some scientis
ts, is global, involving areas of our planet which have not yet been a
ltered by human action. Among the numerous adaptations that make these
amphibians closely dependent on environmental factors there are some
cytogenetic characters. It is well-known that these vertebrates exhibi
t genome sizes covering the widest range of values in the subphylum. V
ariations in their nuclear DNA amount appear to be inversely proportio
nal to changes in their cell metabolic rate and parallel the occurrenc
e of heterochrony during morphogenesis. In urodeles, the largest genom
es are shown by permanently neotenic species or by species involved in
wide ontogenetic repatterning by progenesis. In anurans, the range of
variability is more restricted; however, the largest genomes are foun
d in terrestrial species with direct development, undergoing progeneti
c processes. Therefore, in amphibians, adaptation appears to involve a
lso their nuclear characters; the rapid environmental changes occurrin
g in the last decades may affect also the cytogenetic characters of th
ese organisms, and contribute to their global decline.