SUMMARY A recombinant interferon (IFN) hybrid has been found to have a broad host-range of activity in an antiviral assay (plaque reduction of vesicular stomatitis virus) and also high efficacy as an antiviral agent in at least 12 different animal cell species. The IFN hybrid consists of amino acids 1 to 60 from HulFN-c~B and amino acids 61 to 166 from HuIFN-c~D. The profile of cross-species activity of the IFN-,B/D hybrid has been compared with that of HulFN-c~F, and of the parents HulFN-c~B and -c~D. When both IFN-c~B and -aD were active in a cell species, the hybrid IFN had comparable or better activity than the more active parental IFN. The hybrid shared a broad cross-species activity with IFN-c~D. However, the IFN-c~B/D hybrid was 10-fold more active on human cells, 30-fold more active on rabbit cells, and 50-fold more active on mouse cells than IFN-~D.