SF20/25, originally identified as a product of bone marrow-derived stromal cells, was previously thought to support proliferation of lymphoid cells and was designated as interleukin. However, this activity has not been reproducible and the function of this protein is currently unknown. Recombinant human SF20/IL25 protein, fused to His-tag at Nterminus, was expressed in E.coli and purified by using conventional chromatography techniques, after refolding of the isolated inclusion bodies in a renaturation buffer.