In this paper, we introduce a novel Bmp10-conditional allele and define the unique and overlapping roles of these two ligands in angiogenesis, arteriovenous network formation, and HHT pathogenesis by examining vascular phenotypes of Bmp9-null, Bmp10-iKO, and Bmp9/10-double KO mice. The gene discussed is BMP10; the disease is hereditary hemorrhagic telangiectasia.