Interferon regulatory factor 7 (IRF7) gene was cloned from a subtractive cDNA library constructed with mRNAs obtained from rainbow trout (Oncorhynchus mykiss) macrophage cell line (RTS-11). Using expressed sequence tag clones of submitted IRF7 amino acid sequences, specific primers were designed. Results showed that IRF7 cDNA contains an ORF of 1251 nucleotides that translates into a 416 residues putative peptide. The 5' untranslated region containing 102 nucleotides and the 3' UTR of the transcript consists of 645 nucleotides. The start codon of this ORF is located at nt 103 to 105 and lies in favorable sequence context for the initiation of translation. Alignment between the rainbow trout IRF7 and others IRF7s indicated that the predicted trout IRF7 association domain was located in residues 204-371 aa. The rainbow trout IRF7 nucleotide sequence is most similar to fish IRF7 with 41% identity for crucian carp, Carssius auratus, 45% for zebrafish, Danio rerio, and to mammalian IRF7 with 23% for human, Homo sapiens and 7% for mouse, Mus musculus identity overall.