Endoglin is a homodimeric membrane glycoprotein primarily associated with human vascular endothelium. It is also found on bone marrow proerythroblasts, activated monocytes and on lymphoblasts in childhood leukemia. Endoglin has recently been described as a component of the transforming growth factor-beta (TGF-beta) receptor system as it can bind TGF-beta 1 with high affinity. We now report on the localization of the human endoglin gene (END) to human chromosome 9, by Southern blot analysis of BglII fragments of DNA from human-hamster somatic cell hybrids. This chromosomal localization was confirmed by fluorescent in situ hybridization coupled with Distamicin A (DA)/4',6-diamidino-2-phenylindole (DAPI) banding on human chromosomes. The regional localization was assigned to 9q34-->qter by GTG-banding (G-banding by trypsin using Giemsa stain), indicating a telomeric position with respect to the Philadelphia breakpoint.