cDNA clones containing the entire sequence of the precursor of rabbit tumor necrosis factor (TNF) were identified from a cDNA library prepared using poly(A)+RNA of lipopolysaccharide-induced rabbit alveolar cells. Synthetic oligodeoxynucleotides based on the amino acid sequence of rabbit TNF were selected by RNA blot hybridization and used as probes to screen this library. The DNA sequence and the amino acid sequence deduced from it showed very high homology to the reported DNA and amino acid sequences of human TNF. A plasmid containing the tac promoter and cDNA sequence coding for the 154-amino-acid sequence of mature rabbit TNF protein was constructed and expressed in Escherichia coli. The polypeptide produced had the characteristics of purified rabbit serum TNF and caused a necrotic response in a transplanted syngeneic tumor in mice.