Gene I and II for human nerve growth factor β-subunit (hNGF) (118 amino acids) were synthesized by enzymatic joining of 45 oligodeoxynucleotides with chain lengths of ca. 17, which were obtained by the phosphotriester solid-phase synthesis. Gene I contained the methionine codon downstream of a restriction site, Cla I, for direct expression under the control of E. coli trp promoter, inserted in a plasmid pGH-L9 (M. Ikehara et al., Proc. Natl. Acad. Sci., 81, 5956 (1984)). Gene II coded for a fused protein containing two-thirds of human growth hormone as well as the sequence Ile-Glu-Gly-Arg, in front of the amino acid sequence of hNGF. Both genes were amplified in E. coli by ligation to restriction sites for Cla I and Sal I of pGH-L9 followed by transformation of E. coli. The molecular weight of the expressed products was estimated by electrophoresis on acrylamide gel. The structure of the gene was characterized by restriction analysis and sequencing.