Interleukin-2(IL-2) exerts many immunological responses. To study in in vivo as well as in vitro action of IL-2, we have produced recombinant IL-2 in E. coli previously. The IL-2 was produced in the form of insoluble inclusion bodies in E. coli. Production of IL-2 in E. coli as a soluble protein would increase the specific activity of purified IL-2. Since the codon usage of human IL-2 gene was very different from the preferred codons of E. coli, we attempted to change the IL-2 gene using the E. coli codons. A synthetic gene coding for IL-2 was constructed using the oligonucleotides synthesized by an automatic DNA synthesizer. The nucleotide sequence of the synthetic gene was chosen considering the preferred codons of E. coli by not changing the amino acid sequence of IL-2 polypeptide. The levels of IL-2 expression from the synthetic and the natural gene were compared using the expression vectors with similar constructs. Details will be discussed.