A human liver cDNA library was constructed by using poly(A)-containing RNA isolated from a human liver biopsy specimen. This library is comprised of 40,000 independent transformants with an average inserted DNA length of 1,200 base pairs. By using the previously cloned baboon antithrombin III cDNA as a specific hybridization probe, greater than 30 human antithrombin III cDNA clones were identified from this library. The clone with the longest DNA insert was selected for sequence analysis. This antithrombin III cDNA clone contains 1,479 base pairs of inserted human DNA and was designated phATIII 113. It contains DNA sequences that code for a signal peptide and the entire mature antithrombin III protein which is comprised of 432 amino acid residues.