The extraction equilibrium of zinc in ammonium chloride medium with CYANEX 923 (phosphine oxides mixture) in Solvesso 100 has been investigated. The distribution coefficient of zinc was independent of the equilibrium pH; this independence being attributable to a solvation extraction mechanism. Slope analysis for the system using dilute zinc solution reveals that two motes of CYANEX 923 react with one mot of zinc. The stoichiometric factor of water in the extraction reaction is found to be 2, whereas experimental data indicated that two chloride ions are involved for each metal extracted. The extraction reaction is exothermic (DeltaH degrees = -42.0 kJ mol(-1)).