The dpp/BMP family of TGF beta-related factors controls numerous events in pattern formation and morphogenesis. How these polypeptide signals are received and transduced by target cells is largely unknown. We combine molecular and genetic approaches to establish that the Drosophila saxophone (sax) gene encodes a dpp receptor. We compare the structural properties and expression patterns of sax with a second dpp receptor encoded by the thick veins (tkv) gene. While the sax gene is expressed ubiquitously, tkv is expressed in a highly localized and dynamic pattern during development. Some, but not all, of the tkv expression pattern parallels that of dpp. Ubiquitous expression of a tkv transgene rescues both tkv and sax loss-of-function mutations. Thus, there is at least partial functional overlap of the sax and tkv receptors in vivo. We consider these observations in terms of possible ligand-receptor interactions during Drosophila development.