A rat homologue cDNA of mouse (Koenig et al. [1994] Mol. Cell Biol. 14:5961-5974; Suzuki et al. [1994] Proc. Natl. Acad. Sci. USA 91: 10255-10259) and human (ten Dijke et al. [1994] J. Biol. Chem. 269:16985-16988) type I receptors for BMP-2 and BMP-4 was cloned. Tissue distribution of the receptor mRNA was studied by in situ hybridization using rats at embryonic days 9, 13, 15, and 18 as well as 1- and 5-day-old postnatal rats. In the rats at embryonic days 9, 13, and 15, the receptor mRNA was diffusely expressed over the embryonic bodies. At embryonic day 18, the receptor mRNA expression was high in the hair and whisker follicles, tooth bud, cartilage, bone, digestive organs, lung, kidney, heart, and meninges. The receptor mRNA was expressed over a much wider area than those of the ligands in many organs. In the lung and digestive organs, the receptor mRNA was diffusely expressed and most highly expressed in the bronchial epithelium and muscle layer, respectively, in both of which mRNA expression of the ligands was undetectable. The receptor mRNA was highly expressed in the meninges, although neither of the ligands was expressed in or near this region. These results suggest that this receptor participates in both mesoderm formation in early embryogenesis and differentiation of mesodermal cells during maturation of organs, and further suggest the presence of another factor(s) that binds the type I receptor.