DNA synthesized by in vitro reverse transcription of the interferon mRNA has been cloned and amplified as recombinant DNA, TpIF319-13 (Taniguchi et al., 1979). The nucleotide sequence of this IF cDNA which consists of 770 bp (excluding the A:T tails) has been determined. The data reported predict the hitherto unknown amino acid sequence of human fibroblast interferon and its putative signal peptide.