The strong influence of electrolytes on the partition behavior of charged species is demonstrated in aqueous and aqueous-organic two-phase systems used for extraction. The effects are modeled with an extended Albertsson model which takes into account the electrostatic potential difference between coexisting phases. The partition coefficient of a species regarded may change by a factor of 50 by the addititon of different salts. The electrostatic potential close to the interface is then described by direct integration of the Poisson equation. The results agree with those for the Galvani potential between the bulk phases obtained from the Albertsson model. The influence of ionic species including surfactants on the mass transfer in extraction is discussed. Finally, the coalescence of Liquid dispersions is investigated with electrolytes present in the system. The settling times can be varied by a factor of 1000 in some systems, if appropriate salts ave added at concentrations around 1 mol/m(3). The experimental results are again interpreted on a microscopic level on the basis of the diffusive double layers at the interface.