Hybrids between different Aegilops species and Secale cereale were studied at metaphase I by means of a C-banding technique. On the basis of differences in the C-banding patterns of some of the chromosomes of these hybrids it was possible to carry out an accurate analysis of several types of Aegilops-Aegilops and Aegilops-Secale chromosome associations and, consequently, to establish intraspecific and intergeneric genome relationships. Genomes present in the majority of polyploid Aegilops species are shown to maintain similar patterns of evolutionary affinity to those reported for their proposed diploid parents although in some species there are differences indicating either that differentiations occurred during the evolution of the polyploid species or, on the contrary, that the diploid donors proposed are not the correct ones. On the other hand, differences in the relationships not only between the R genome and different Aegilops genomes but also among different homoeologous groups have been found.