Sequence determination of cloned cDNAs and genes of the three classes of interferon (IFN-α, -β and -γ) has revealed more than a dozen members of the human IFN-α gene family1-7 and a single gene for IFN-β4,8-14. These genes are found on chromosome 9 (ref. 15) and contain no introns1,5-7,11-14. We recently reported16 that the 146-amino acid sequence of mature IFN-γ deduced from the nucleotide sequence of a cloned cDNA was quite unrelated to those of the other IFNs, and that the gene for IFN-γ contains at least one intron16. We now describe the isolation, characterization and DNA sequence of the human IFN-γ gene. It contains three introns, a repetitive DNA element, and is not highly polymorphic. All our evidence to date16,17 and the present data suggest that this is the only gene for IFN-γ and that the resolution of IFN-γ into two components18 is probably the result of post-translational processing of the protein.