Hybridization sites of an rDNA probe coding for the 5.8S, 18S and 26S genes were detected on the chromosomes of sugarcane and a related genus, Erianthus, using fluorescence in situ hybridization. One unpaired and five paired hybridization sites were detected in a Saccharum spp. hybrid. A first introgression hybrid (I1) between Saccharum officinarum and Saccharum spontaneum had seven pairs of hybridization sites. A clone of Erianthus arundinaceus showed six hybridization sites in somatic tissue.