Complex coacervation between oppositely charged albumin and acacia mixtures has been studied, and the applicability of the various theoretical treatments of complex coacervation (the Voorn-Overbeek, Veis-Aranyi, Nakajima-Sato, and Tainaka theories) to this system has been assessed. Under optimum conditions where maximum coacervate yield occurred, the Voorn-Overbeek theory appeared to apply. However, away from the optimum coacervation conditions, coacervate sol formation was observed, which is in accordance with the Veis-Aranyi and Tainaka theories. Microelectrophoretic measurements were used to determine optimum pH and ionic strength conditions for maximum coacervation, based on the method of Burgess & Carless (1984). The effects of pH and ionic strength on coacervate yield are reported. Around the optimum conditions for maximum coacervation a viscous coacervate phase and a relatively clear equilibrium phase are formed.