Mitotic chromosomes of 16 species of the frog genus <i>Xenopus</i> were prepared from kidney and lung cell cultures. In the chromosomes of 7 species, high-resolution replication banding patterns could be induced by treating the cultures with 5-bromodeoxyuridine (BrdU) and deoxythymidine (dT) in succession, and in 6 of these species the BrdU/dT-banded chromosomes could be arranged into karyotypes. In the 3 species of the clade with 2n = 20 and 4n = 40 chromosomes (<i>X. tropicalis</i>, <i>X. epitropicalis</i>, <i>X.</i> new tetraploid 1), as well as in the 3 species with 4n = 36 chromosomes <i>(X. laevis</i>, <i>X. borealis</i>, <i>X. muelleri)</i>, the BrdU/dT-banded karyotypes show a high degree of homoeology, though differences were detected between these groups. Translocations, inversions, insertions or sex-specific replication bands were not observed. Minor replication asynchronies found between chromosomes probably involve heterochromatic regions. BrdU/dT replication banding of <i>Xenopus</i> chromosomes provides the landmarks necessary for the exact physical mapping of genes and repetitive sequences. FISH with an <i>X. laevis</i> 5S rDNA probe detected multiple hybridization sites at or near the long-arm telomeric regions in most chromosomes of <i>X. laevis</i> and <i>X. borealis</i>, whereas in <i>X. muelleri</i>, the 5S rDNA sequences are located exclusively at the long-arm telomeres of a single chromosome pair. Staining with the AT base pair-specific fluorochrome quinacrine mustard revealed brightly fluorescing heterochromatic regions in the majority of <i>X. borealis</i> chromosomes which are absent in other <i>Xenopus</i> species.