The extraction of 0.05 and 1mgmL-1 human IgG4 using reverse micelles (RMs) formed with anionic surfactants AOT or HDEHP in isooctane was evaluated. For both surfactants the use of 1mgmL-1 IgG4 resulted in higher forward extraction (FE), and generally better backward extraction (BE) yields than 0.05mgmL-1 IgG4, achieving optimum FE and BE yields at FE pHs of 5 at 3.13mM AOT and 6 at 1.56mM HDEHP. IgG4 precipitation at the interface was observed at the lower pHs during FE which appeared to cause low overall extraction yields. Water content analysis revealed AOT-RMs were much bigger than HDEHP-RMs.