A novel recombinant dual human stem cell factor (rdhSCF) gene which consisted of a full-length hSCF(1-165 aa) cDNA and atruncated hSCF (1-145 aa) cDNA, linked by a peptide (GGGGSGGGGSGG) coding region, was constructed and cloned into Escherichia coli expression vector pET-22b. The rdhSCF was expressed at high level in E. coli BL21(DE3) and existed mainly as inclusion bodies. The inclusion bodies were solubilized in urea and refolded by ion-exchange chromatography. After renaturation, the purity of the yielded rdhSCF was up to 90%. Cell proliferation assay showed that the specific activity of the rdhSCF was 2.86 x 10(5) U/Mg, about 1.66 times as high as that of monomer rhSCF expressed in E coli. (c) 2005 Elsevier Inc. All rights reserved.