Fish interferon (IFN) cDNA was first cloned from the cDNA library of immortalized flatfish leukocytes. The clone contains an open reading frame that encodes a 138 amino acid polypeptide including a glycosylation site and a signal peptide containing 30 amino acids. BHK-21 cells transfected with the INF-expression plasmid produced active recombinant IFN (about 16 kDa) which was then purified by WGA agarose affinity chromatography. This recombinant IFN inhibited infection of fish cells with the Hirame (flatfish) rhabdovirus.