Human platelet glycoprotein Ib beta (GPIb beta) (M(r) 22,000) is part of the GPIb-V-IX system that constitutes the receptor for von Willebrand factor and mediates platelet adhesion in the arterial circulation. The four members of the receptor (GPs Ib alpha, Ib beta, V, and IX) share structural and functional features. Individually, GPIb beta contributes to surface expression of the receptor and participates in transmembrane signaling through phosphorylation of its intracellular domain. To define the structure of the GPIb beta gene, a cosmid clone from a human genomic library was analyzed. The transcriptional start site was located by both primer extension and the "anchored" polymerase chain reaction. Similar to the genes for Ib alpha, V, and IX, the Ib beta gene is compact with a single 274-base intron inserted into the 5' end of the open reading frame. The 5'-flanking region of the gene contains both GATA and ets sites that are also found in the 5' promoter regions of other described megakaryocyte/platelet genes. The GPIb beta gene was localized to chromosome 22q11.2 by fluorescence in situ hybridization. The GPIb beta gene has a simple structure, similar to that of other described megakaryocyte/platelet genes, including those of the GPIb-V-IX system.