Abstract: Exogenic porcine interferon for administration in human beings. The porcine interferon shows antiviral protecting activity on cultured human cells and is substantially free of any immunoelectrophoresis bands which are not identical or partially identical with bands in human leucocyte interferon or human agammaserum. A process for preparing the porcine interferon by harvesting, isolating and, if desired, priming porcine leucocytes, treating them with an interferon inductor and incubating them and obtaining the interferon formed, the process being characterized in using, as added protein source in any of the said stages, a source which is substantially free of immunoelectrophoresis band which are not identical or partially identical with bands in human agammaserum.