A cytogenetic study, based on the comparative analysis of chromosome morphology, amount and distribution of C-positive heterochromatin and positions of NORs, was undertaken on three species of brown frogs (Rana temporaria, R. dalmatinaandR. graeca) from different Balkan localities. In contrast to their uniform karyotypes with respect to chromosome number, important interspecies differences have been observed in centromeric indices, the amount of constitutive heterochromatin, the distribution of C-bands and the positions of NORs. Analysis of these karyotype characteristics suggests that mostly intrachromosomal rearrangements occurred during karyotype differentiation of the examined species.