This contribution concerns chemical mass transfer between liquid phases with the main question directed to the action of adsorbed amphiphilic layers at the interface. As the model system, the complexation of zinc ions (aqueous phase) with dithizone (toluene phase) was selected, measured with the stirred cell technique. This allows the discrimination of flow-dependent transport processes from the flow-independent interfacial reactions as the rate-controlling alternatives. In the absence of surfactants (the so-called base system) the measured rate of mass transfer is shown to be limited by transport processes or interfacial reactions, depending on the level of the zinc ion concentration. In the regime of slow interfacial reactions for the interfacial flux, a linear dependency of the zinc ion and the dithizone concentration and a reciprocal first-order influence for the proton concentration were observed. Because the interaction of amphiphilic layers with the interfacial reaction was the main point of interest, only cases of mass transfer being independent of convection are taken into consideration. For this regime it was shown for the first time that the presence of anionic adsorption layers alters not only the rate constant but first of all the mechanism of the occurring interfacial reaction. The striking results concern the appearance of a saturation kinetic related to the zinc ion concentration, the disappearance of the proton sensitivity, and a strong rate inhibition by added electrolytes. Moreover, the interfacial layer acts as an accelerator or as an inhibitor for the controlling interfacial reaction, depending on the zinc ion concentration. A kinetic model is proposed which explains most of the experimental results in a plausible manner. Because of the observed equivalent action of BOT (bis(2-ethylhexyl) sulfosuccinate sodium salt) and SDS layers (sodium dodecyl sulfate), it seems justified to assume the possibility of a strong interaction of interfacial reactions with anionic monolayers as a frequent feature. Preliminary measurements concerning the action of the cationic surfactants demonstrate a behavior consistent with the interpretation pattern : The fluxes of the base reaction are inhibited by electrostatics.