Chemical studies show that there are close relationships between the storage proteins of the Triticeae. We have investigated these relationships by the study of the synthesis of the proteins in vivo and in vitro, and by making libraries of double-stranded complementary DNA (cDNA) derived from poly A<latex>$^+$</latex> RNA isolated from developing endosperms of barley, wheat and rye. These cDNA clones have been used to probe the organization and regulation of expression of the Hor loci in barley. The results suggest that regulation of synthesis is generally achieved by changes in the amounts of mRNA for the different proteins, both in response to time of development and the relative supply of sulphur and nitrogen, although there may also be differences in the relative amounts of mRNA translated. The sequencing of the cDNA clones has shown the importance of repeated sequences in the evolution of prolamin genes.