The mechanism of mass transport at liquid/liquid microinterfaces formed in cylindrical microholes is discussed and a model for the diffusional transport is developed. It reveals, that the half-wave potential of the ion transfer depends on the hole diameter and the foil thickness. The theory has been verified by voltammetric measurements using different hole diameters in polymer foils of 12 mu m thickness. The standard Gibbs energies evaluated by using the theoretically derived equation are comparable with results presented in the literature for experiments performed at interfaces of conventional size and with data obtained from extraction measurements. (C) 1998 Elsevier Science Ltd. All rights reserved.