We have investigated a novel microfiltration process for the separation of plasma from whole blood to act as the primary stage of a membrane-based affinity system. The combination of oscillatory flaw, with a small mean flow component and flow deflectors have been employed to generate a vortex wave in a flat membrane channel. The vortex wave has been analysed under predominantly laminar flow conditions such that the design is appropriate for shear-sensitive fluids. The performance has been assessed in terms of long term plasma filtration rates, the level of blood damage and total protein recovery. The vortex wave produces an enhancement factor of 3.5 relative to a flat unobstructed channel at Re = 123. Membranes of 0.2 mu m and 0.45 mu m pore sizes gave very similar trends in terms of plasma flux, haemolysis rate and total protein sieving coefficients. Detailed explanations are given for the influence of Reynolds number, Strouhal number, deflector spacing and mean flow rate on plasma flux, At plasma filtration rates as high as J = 0.1 cm/min blood damage was found to be negligible.