The structure of the IFN alpha receptor has been studied by methods such as affinity crosslinking and gel chromatography over the last 8 years. The recent development of monoclonal antibodies against the receptor, and the cloning of an IFN alpha receptor cDNA has provided new important tools to understand the IFN alpha receptor structure. Thus, it has become obvious that the IFN alpha receptor has a more complex structure than first anticipated, probably involving more than one subunit. This review analyzes the present knowledge about the structure of the IFN alpha receptor, as well as many unresolved issues concerning this topic.