Abstract: The invention provides cell culture methods that efficiently produce new infectious HCV virions where such methods are based on the unexpected finding that culturing cells at lower temperatures, i.e., from about 20° C. to about 34° C., enables efficient methods dependent upon HCV E1E2 mediated fusion. The invention also provides fusion assay methods that are robust and reliable because of, at least in part, specific pH conditions, and HCV E1 and E2 proteins that contain a dimerization domain. The present methods are useful for propagating infectious HCV, for improved diagnostics, drug screening and basic research efforts relating to HCV receptor binding, HCV entry (binding (attachment) and fusion), replication, virion assembly and release. In another respect, the present invention provides methods for detecting HCV E1E2 mediated fusion, and related methods for identifying drugs or other molecules that can inhibit HCV fusion and for identifying mutations that can inhibit HCV fusion.