Swine IL-7 (sIL-7) cDNA has been isolated from neonatal intestinal epithelium by reverse transcription polymerase chain reaction (RT-PCR) with designated primers based on the conserved sequences of the other mammalian IL-7. Recombinant sIL-7 was able to induce the bone marrow cell proliferation like human IL-7. The complete open reading frame contains 531 bp coding deduced 176 amino acid residues, with a calculated molecular mass of 20.1 kDa. The observed similarity between swine and human IL-7 sequences (66% identical and 89% conserved) suggests that a study on the immune responses correlated with IL-7 in the gut of swine will be valuable to understand their mechanisms in human. By RT-PCR using the constructed specific primers to sIL-7, sIL-7 mRNA was confirmed to be expressed in swine intestine, thymus, kidney and skin but not in the heart.