Direct restriction analysis of the human genome, using the Southern transfer technique and hybridization with a human fibroblast interferon (IFN-beta) complementary DNA insert probe, revealed the presence of a single gene; no additional closely related IFN-beta genes could be detected. A lambda-linked human gene library (Lawn et al., Cell, 15, 1157-1174 (1978)) was screened using the cDNA probe. Out of 600,000 recombinant phage examined, one single clone bearing interferon sequences was obtained. Restriction analysis of the relevant region revealed an identical restriction map as obtained for the IFN-beta 1 cDNA clones. No intervening sequences could be detected, either in the coding or the non-coding regions of the gene.