Mammalian hepcidin is an antimicrobial peptide and a key regulator in the iron homeostasis. Here we report the identification and cloning of a hepcidin cDNA from Atlantic cod (Gadus morhua L.). The cod hepcidin cDNA was predicted to encode a prepropeptide of 98 amino acids (aa) with a signal peptide of 22 aa. A tentative RX(K/R)R motif for propeptide convertases was also identified suggesting a cleavage site located between Arg(72) and Gln(73). The deduced mature cod hepcidin sequence of 26 aa shows similarity to other reported hepcidins and the gene organization is also similar to corresponding genes in mammals and fish consisting of three exons and two introns. As reported for most other species, the expression level of cod hepcidin was highest in liver. However, high levels of hepcidin expression were also observed in the head kidney and peritoneum and an upregulation of hepcidin transcription was seen in all tissues examined 2 days after i.p. injection of formalin-inactivated Listonella (Vibrio) anguillarum. Poly I:C was also able to induce hepcidin transcription. In situ hybridization showed a leukocytic morphology and localization of hepcidin-positive cells in several tissues, and the expression data imply that cod hepcidin is an important component of the first-line defense against invading pathogens.