Cultivated banana, Musa spp., there are four known genomes, A, B, S, and T. These correspond to the genetic constitutions of wild Eumusa species M. acuminata, M. balbisiana, M. schizocarpa and the Australimusa species, respectively. Most cultivated clones are triploid or diploid, they have been classified into genomic groups according to chromosome numbers and morphological traits. Genomic in situ hybridization (GISH) enabled us to differentiate the chromosomes of these four genomes; however, a distal portion of the chromosomes remained unlabelled. GISH was used to determine the exact genome structure of interspecific cultivated clones. In most cases the results were consistent with the chromosome constitution estimated by means of phenotypic descriptors. The one notable exception, the clone 'Pelipita', has the 8 A and 25 B chromosomes instead of the predicted 11 A and 22 B. GISH also enabled us to determine the chromosome complement of a few clones that could not be classified only on the basis of phenotypic descriptors and chromosome counts. The rDNA sites were located in Musa species. They appeared to be often associated with satellites, which can be separated from the chromosomes, representing a potential source of error for chromosome counting using classical techniques.