The present invention .relates to a process to isolate genetic material (DNA) containing the nucleotide sequence coding for interferon in human fibroblastic cells which comprises cultivating cells producing interferon when exposed to an inducer of interferon, exposing same to such inducer, extracting messenger RNA from said induced cells, purifying the interferon messenger RNA, transcribing the messenger RNA into DNA and cloning the DNA in a suitable vector. Preferred cells are human diploid foreskin cells. The invention further relates to a process for engineering a bacterial strain to produce interferon polypeptide which comprises introducing a cloned interferon DNA into a suitable vector-carrier. A preferred vector-carrier is E. coli. The invention also relates to the mRNA of human interferon in highly purified form, to the mRNA of human interferon in .beta.1 highly purified form, to the mRNA of human interferon in .sym.2 highly purified form, to the DNA coding for a polypeptide having interferon activity, insertable in a vector, such as plasmid pBR322, and also to human interferon .beta.1 in highly purified form, and human interferon .beta.2 in highly purified form.