BACKGROUND: Human granulocyte-macrophage colony stimulating factor (hGM-CSF) is a kind of cytokine which can stimulate the differentiation and proliferation of haematopoictic precursor cells and plays an important role in the process of immunoloregulation. Escherichia coli (E.coli) expression system has advantages,such as low cost and high output, over other systems.Therefore, E.coli is still the most commonly used exogenous gene expression system.OBJECTIVE: To observe the expression of hGM-CSF in the E.coli swain DH5α.DESIGN, TIME AND SETTING: The present observational experiment was performed at the Central Laboratory of Biotechnology Research,China Three Gorges University between February and June 2007. MATERIALS: Plasmid pBR322hGM-CSF was purchased from American Type Culture Collection, USA.hGM-CSF antibody was sourced from Sigma Company, USA.IPTG, X-gal,and vector pMGT-18 were purchased from Shanghai Bioengineering Technology Company, China. METHODS: Primer was designed according to hGM-CSF gene. Taking cloning vector plasmid pBR322-hGM-CSF as template, hGM-CSF gene was acquired and recombined into prokaryotic expression vector pGEX-4T-1. Recombinant plasmid confirmed by enzyme digestion and sequencing was transformed into E.coli strain DH5α and induced by isopropy-β-D-thiogalactoside (IPTG). Expression product was identified by sodium dodecyl sulfate polyacrylamide gel electropheresis (SDS-PAGE) and detected by Western blotting assay. MAIN OUTCOME MEASURES: hGM-CSF expression in the E.coli strain DH5α. RESULTS: SDS-PAGE results revealed that the recombinant hGM-CSF protein with relative molecular weight of 40 500 was produced up to approximately 17.9% of total protein. Western blotting detection results indicated that there was a 40 500 bp brand. CONCLUSION: The present study reconstructed prokaryotic expression vector pGEX-hGM-CSF, induced its expression in the E.coli strain DH5α, and obtained hGM-CSF fusion protein.