To develop detailed linkage maps of restriction fragment length polymorphism (RFLP) sites in wheat chromosomes, it was necessary to construct a genomic DNA library and to characterize the clones obtained. Forty-nine per cent of the clones were of single or low copy number per genome. With 91 clones of this class, as probes, and with two to four restriction endonucleases, for DNA digestion, RFLPs were examined among eight common wheats and a single emmer wheat. About 20% of the probes, and 13% of the probe-enzyme combinations revealed genetic polymorphism among the common wheats. DNA deletions account for most of the genetic differences among these wheat genomes. Based on the RFLP data, phylogenetic distances among the nine polyploid wheats were estimated, and a dendrogram showing the genetic relationships among them was constructed.