We have constructed three different plasmids containing parts of the human growth hormone gene using chemically synthesized oligomers and cloned them for the purpose of expressing them in Escherichia coli. AB, B and BC gene segments corresponding to ABhGH (residue 1-138), BhGH (residue 44-138) and BChGH (residue 44-192) were placed under the control of a tryptophan promoter in the expression vector. Upon induction with 3-indolylacrylic acid, ABhGH accumulated in cells but the BhGH and BChGH segments were not detected appreciably. Northern blotting analysis showed that the amount of mRNA transcribed from the AB gene segment was about ten-fold higher than that from the B or BC gene segment. ABhGH was found to have insulin-like growth factor I (IGF-I) activity, which could be explained by the hydrophilicity curves of these proteins.