In this communication we demonstrate a conception of an artificial microkidney using pertinent microtools that more accurately mimic organ functions in vitro. We present a technique to integrate polyethersulfone (PES) membranes usually used in hemodialysis inside a polydimethylsiloxane (PDMS) microchip. The purpose of the microchip is to model glomerular filtration "on-chip". Mass transfer of urea (60 Da), vitamin B12 (1355 Da) and albumin (70,000 Da) are investigated by using two types of membranes (cut-off at 500,000 Da and 40,000 Da) in co-current and counter-current flow conditions. The time of urea, vitamin B12 and albumin removal, and the mechanisms of mass transfer, are controlled either by controlling the pore size of the membranes or by controlling the pressure profiles along the membrane via the flow conditions. An analytical model, which is supported by our data, is put forth. The model allows the extraction of the diffusion coefficients of each molecule through the various membranes studied. Due to the downscaling, the model and the experiments demonstrate that the dialysance in the microchip is expressed by the sum of the diffusion and convection mass transfer components. The results of this work support an analytical model which describes the mass transfer in a microchip modelling a glomerular unit. Coupled with the advantages of the microfluidic biochip (high surface/volume ratio, reduction of the fluid volumes), our data will complete the integration of further cellular functions for the utilisation of the present microchip as a future in vitro model of a miniaturized bio artificial kidney. (C) 2010 Elsevier B.V. All rights reserved.