A new technique for investigating kinetics in and transport between two liquid phases is described. The interface of known area is established on the sinter in a Stokes diffusion cell. Transport to the interface is controlled by diffusion across the sinter. The rate of a reaction can be controlled by transport across the sinter, the reaction at the interface, by a slow transfer across the interface or by homogeneous reaction in either phase. Each of these cases can be described theoretically. Results are reported for the hydrolysis of p-methylbenzyl chloride and of methyl nicotinate in water/CCl4 and water/isopropyl myristate. Reasonable agreement with theory is found. For methyl nicotinate the rate determining process is diffusion across the sinter. For p-methylbenzyl chloride the rate determining process is the transfer of the substrate from the organic phase to the aqueous phase. Rate constants for the interfacial transfer process in both directions are reported and discussed.