Recently, we proposed a novel preparative free flow zone electrophoresis cell with extremely short residence time, which does not require external cooling (Poggel, M., Melin, T, Electrophoresis 2001,22,1008-1015). Within the new cell the smallest chamber dimension is not orientated perpendicular but in direction of the electric field. This alteration provides straight forward scale up opportunities. In this paper, new experimental results are reported, from which the limits of stable flow can be determined. The data suggest that not density differences but electrohydrodynamic effects are responsible for the disturbance of the laminar flow pattern, which is observed above a critical field strength. To demonstrate the efficiency of the new system, a three-component mixture consisting of bovine serum albumin (BSA), myoglobin and cytochrome c is processed, resulting in relatively high recovery and purity values of the different proteins, although a complete separation is not achieved.