HuIFN-alpha has been found to consist of a family of 8-10 components. Their amino acid (165 and 166 residues) and nucleotide sequences are similar and also reveal some relationship to that of HuIFN-beta and even to those of murine alpha- and beta-interferons. It is thus likely that all mammalian interferons have originated from a common ancestral gene. Human beta- and some alpha-interferons have been obtained by genetic engineering in E.coli. All interferons seem to contain a relatively high proportion of hydrophobic amino acids and some of the components are glycosylated. The N-terminal residue of all HuIFN-alpha members is probably cysteine, that of the major HuIFN-beta peptide methionine and that of MuIFN-alpha and-beta probably alanine and isoleucine. Very little is known about the chemistry of any of the gamma-interferon species.