Chromosome relationships in allopolyploid species are either homologous, homoeologous, or non-homologous. To discern the behavior of chromosomes in each of these relationships, we produced double monosomic addition lines (DMAs) of wheat carrying one Leymus racemosus chromosome and one Leymus mollis chromosome in different combinations, and observed the Leymus chromosomes in meiosis by differential genomic in situ hybridization. First we observed the distribution of these alien chromosomes in tetrad cells and measured their homology by an index of their interaction. Values differed greatly among DMAs. We observed prophase to anaphase cells of meiotic division I and elucidated the differences in homology through chromosome behavior in meiosis. A line carrying chromosomes [l^r] of L. racemosus and [M^m] of L. mollis formed bivalents in about half of the prophase cells, but these chromosomes became univalent in metaphase because of a lack of chiasmata, and segregated normally to each pole. The chromosomes in the other half of the prophase cells did not associate and behaved randomly from anaphase to tetrads. The DMAs proved useful in studying the homology of chromosomes.