An 18 residue amino terminal sequence of the barley endosperm protein Z polypeptide is presented. In vitro translation of barley endosperm mRNA and subsequent immunoaffinity isolation using protein Z antibodies identified two major protein Z precursor polypeptides of M.W.44,000 and 46,000 among the translation products. Partial nucleotide sequence analysis identified a cDNA clone to encode the amino terminal portion of protein Z. Messenger RNA sequences 1,800 nucleotides in length, sufficient to code for the protein Z precursor polypeptides, were detected by hybridization to the protein Z cDNA probe. Hybridization of the probe to restriction endonuclease fragments of barley nuclear DNA suggests, that protein Z is encoded by a small multigene family.