Process for the purification of interferon

A process for the purification of interferon consisting essentially of (1) partitioning interferon in an aqueous multi-phase system in the presence of at least one ion exchanger which is soluble in said system selected from the group consisting of (a) polyoxyalkylene glycols and (b) reaction products of polyhydric alcohols with alkylene oxides, which ion exchanger contains at least one carbon-bound group --S.sub.0-1 --Z, wherein --S--Z is a member selected from the group consisting of:

• --NH--(CH.sub.2).sub.1-14 --Z,
• --O--(CH.sub.2).sub.1-14 --Z,
• --NH--CO--(CH.sub.2).sub.1-14 --Z,
• --NH--(CH.sub.2).sub.1-14 --NH--CO--(CH.sub.2).sub.1-3 --Z,
• --NH--CH.sub.2 --CH.sub.2 --(O--CH.sub.2 --CH.sub.2).sub.1-4 --Z and
• --O--CO--(CH.sub.2).sub.1-13 --Z and
• --Z is a member selected from the group consisting of:
• --P(O)(OH).sub.2,
• --O--P(O)(OH).sub.2,
• --O--P(S)(OH).sub.2,
• --S--P(O)(OH).sub.2 and
• their salt forms, (2) separating the phases including an interferon containing phase and (3) recovering purified interferon from said interferon containing phase.