The genus Calomys Waterhouse, 1837 is widely distributed within South America, being found in Venezuela, Colombia, Peru, Bolivia, Brazil, Paraguay, Uruguay and Argentina. Specimens of Calomys were collected in Formoso do Araguaia, Tocantins, Brazil. For chromosome characterization standard staining techniques and as G-banding and nucleolar organizer region were used. The karyotype was 2n=46 and AN=66. The X chromosome is a medium metacentric and the Y chromosome a small acrocentric chromosome. Chromosome homologies with other species were observed. Probably, karyotype differences were basically due to Robertsonian rearrangements.

Cytogenetic studies on Cycloramphus boraceiensis Heyer, 1983 collected in Picinguaba, Ubatuba, State of São Paulo are presented. The species has 2n=26 karyotype formed by metacentrics, submetacentrics, and one telocentric pair which carries Ag-NORs. The C-banding patterns is also described.

Descreve-se a padronização da cultura de linfócitos com a finalidade de melhorar as preparações citológicas de espécies de anfíbios anuros. Esta metodologia permite o uso do tratamento pelo BrdU para se obter padrões de bandas de replicação nos cromossomos dessas espécies.

We describe the standardization of lymphocyte culture procedures in order to improve cytological preparations of anuran species. This methodology permits the use of 5-bromodeoxyuridine (BrdU) treatment to obtain replication banding patterns in the chromosomes of these species.