Aninterleukin-7 (IL-7) gene has been cloned and sequenced within the Japanese pufferfish,Takifugu rubripes(Fugu), providing the first conclusive evidence for the existence of IL-7 in teleosts. The IL-7 cDNA was com-posed of 1438 bp, with a 117 bp 5¢-UTR, an 826 bp 3¢-UTR containing two mRNA instability motifs, and a 498 bp ORF which translates into a peptide of 166 amino acid residues.