Recognition of viral nucleic acids by vertebrate host cells results in the syn-thesis and secretion of type I interferons (IFN-a⁄b), which induce an anti-viral state in neighboring cells. We have cloned the genes and promoters of two type I IFNs from Atlantic salmon. Both genes have the potential to encode IFN transcripts with either a short or a long 5¢-untranslated region, apparently controlled by two distinct promoter regions, PR-I and PR-II, respectively.