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 We studied the expression of human growth hormone (hGH) in E. coli under a bacteriophage T5-base promoter in a pQE30 expression vector. For an: efficient expression of hGH cDNA، a number of codons at the hGH N-terminal coding region were altered based on the E. coli major codons. An over-expression of hGH;in the bacteria، carrying the recombinant plasmids، was observed at 37°C in the presence of IPTG The over-expression was also observed at 30°C in the absence of IPTG. Therefore a temperature down-shift induction، 37°C to 30°C، was suggested to achieve an over-expression of recombinant hGH (rhGH) without the use of chemical inducers. The pQE30-hGH recombinant plasmids show high stability in the TG 1 host in the non-selective conditions. In a batch fermentation condition، the purified rhGH was obtained with the yield of 53 mg/l of culture. We took advantage of the formation of inclusion bodies to recover the rhGH، followed by diafiltration and refolding steps. The purified rhGH was biologically active for its receptor-binding on IM9 cells.