The mechanism of the transfer of zinc(11) between 1.0 M HCl, 6.0 M HCl and 6.0 M LiCl and methyltrioctylammonium chloride in chloroform has been studied by using the single-drop technique. It is suggested that interfacial complexes are formed by fast ion-exchange reactions and that the rate-determining step, in the case of 1.0 M HCl and 6.0 M LiCl, involves the replacement at the interface of the complex R2ZnCl4 by two molecules of reagent from the bulk organic phase. For 6.0 M HCl the rate-determining step is the replacement of the interfacial complex RHZnCl4 by one molecule of reagent from the bulk organic phase. Support for this mechanism is obtained by comparing the extraction equilibrium constants for the complex R2ZnCl4 for 1.0 M HCl and 6.0 M LiCl from previous with the values calculated from the rate data. Interfacial tension measurements have shown that the interface is saturated with reagent over the full range of concentrations studied.