A recombinant human antibody expressed in corn was purified using aqueous two-phase extraction. The antibody was an immunoglobulin C fully unglycosylated. Using systems of different compositions and/or pHs in each of one or two partitioning stages followed by one more stage in which the antibody was precipitated at the liquid/liquid interface facilitated the removal of different impurities in each stage. The best system yields a product 72% pure (22 fold purification) with a yield of 49%. The optimum extraction was clone in two partitioning stages followed by an interfacial precipitation stage using poly(ethylene)glycoll potassium phosphate systems. NaCl wets added to the first stage to eliminate large molecular weight impurities. The pH in the first stage was kept at 6 but a pH of 8 was used in the second stage and in the precipitation stage. (C) 2009 American Institute of Chemical Engineers Biotechnol. Prog., 26: 159-167, 2010