Protein, produced by a bacterial culture of recombinant Vibrio cholerae, was separated from cells in a fermentation broth by cross-flow microfiltration. A new, mechanically agitated (rotational) shear filter, the DMF(TM) filter from Pall, was used to perform the separation. Higher protein recovery and permeate flux than commonly obtained during cell harvesting were demonstrated using sixfold concentration followed by twofold diafiltration. The transmembrane pressure only increased by 10 kPa when the flux was kept constant at 150 L/m(2) h during both concentration and diafiltration. The protein transmission was about 100% initially, and over 90% at the end of the concentration process. The protein transmission during the diafiltration was over 80%. The total recovery of protein was 97%. When using an enzymatic cleaning agent, no significant pure water flux decrease was detected during the course of the experiments.