Karyotype analysis ofBalistes carolinensis, by means of C banding and silver nitrate staining, reveals: 44 acrocentric chromosomes in both males and females; a secondary constriction in the third pair corresponding to the NORs whose position is subcentromeric and C-positive; and a constitutive heterochromatin pattern being mainly distributed in pericentromeric areas of three chromosome pairs. The most important evolutionary implications of these characteristics are: the reduction of diploid number of the species in relation to the ancestral teleost coinciding moreover with the modal value of the group (2n= 44); the parallelism of this reduction with the taxonomical position of the balistids; the scarcity of constitutive heterochromatin in comparison with the most other teleostean species also reflecting a diminution; and the primitive disposition of the NORs. Such characteristics prove specialized among Teleosts but relatively generalized into the order Tetraodontiformes.