A cDNA corresponding to canine IL-2 has been isolated and sequenced. The cDNA was synthesised using RT-PCR, with oligonucleotide primers designed from conserved regions of published IL-2 sequences. The cDNA encodes a predicted full length IL-2 protein of 155 amino-acids. At the nucleic acid level, the canine cDNA shows 92, 88, 88, 82 and 74% homology to published sequences of feline, human, equine, bovine and murine IL-2, respectively. The derived protein shows 90, 86, 85, 76 and 75% similarity to feline, human, equine, murine and bovine IL-2 homologs.