Bone morphogenetic proteins (BMPs) regulate a wide range of cellular functions that contribute to embryonic development from mesoderm formation to organogenesis. BMP type II receptor (BMPR‐II) transduces BMP signals by forming heteromeric complexes with and phosphorylating BMP type I receptors. Heterozygous germline mutations of BMPR‐II gene have been identified in patients with familial and sporadic primary pulmonary hypertension, indicating that BMPR‐II may contribute to the maintenance of normal pulmonary vascular structure and function. Since embryos homozygous for a null BMPR‐II allele died during gastrulation, precluding further studies of BMPR‐II function in organ formation and in adult tissues, we generated mice carrying a conditional mutant BMPR‐II allele in which exons 4 and 5 were flanked by loxP sequences. We anticipate that studies of mice carrying a floxed BMPR‐II allele and a Cre transgene (under the control of a tissue‐specific promoter) will enable characterization of the role of BMPR‐II in specific cell types during development and in the pathogenesis of cardiovascular diseases. genesis 41:133–137, 2005. © 2005 Wiley‐Liss, Inc.