The polymer support method for the oligonucleotide synthesis has been developed and used for the chemical synthesis of a 27-desamidosecretin gene. The gene carrying Pst I recognition sites at both ends was built from 16 fragments and each of them was synthesized by a stepwise addition of protected nucleotides on a polymer support. The coupling yield of each step was almost 90% and after partial deblocking, oligonucleotides carrying trityl groups were purified by chromatography on a reverse phase column. The recombinant DNA containing this synthetic gene was expressed in bacterial cells.