The 873 base pair coding region of a Hor-2 gene of barley and the adjacent 550 base pair upstream and 413 base pair downstream regions were sequenced. The gene is devoid of introns and encodes a 271 amino acid long B1 hordein polypeptide containing a putative 19 amino acid signal peptide. The remaining part of the coding sequence can be divided into three parts. In the 53 residue amino-terminal region there are 9 glutamine-proline blocks with a preferred core sequence PQQP, separated by one or two other residues giving a glutamine proline content of 78%. The second part encodes 164 amino acids, 41% of which are glutamine+proline organised in scattered blocks. Seven cysteine residues are coded for by this portion of the gene. The last part encodes the carboxyterminal 35 amino acids none of which is glutamine. In the 550 base pair upstream region the sequence TATAAATA is found at- 71 base pairs from the initiator methionine. In the 3′ non-coding region three putative polyadenylation signals, AATAAA, are present. Comparison of the gene with 3 partial cDNA clones indicates that the charge polymorphism in the B1 polypeptide group is due to point mutations in the part of the gene corresponding to the carboxy terminal half of the polypeptide. Comparison with the sequence of a second B hordein gene suggests that insertions or deletions of glutamine-proline blocks in the amino-terminal domain are a major source of size polymorphisms in the B hordein family.