A gene for human tumor necrosis factor has been synthesized by joining 60 oligodeoxyribonucleotides of 13 to 20 residues using deoxyribonucleic acid (DNA) ligase. These oligodeoxyribonucleotides were prepared by the solid-phase phosphotriester method. The gene (483 base pairs) was designed to carry a Cla I site plus a start codon at the N-terminal end and stop codons plus a Sal I site at the C-terminal end. The gene was expressed in Escherichia coli under the control of the tryptophan promoter of E. coli, and the expressed product was purified and tested for cytotoxic activity.