Simultaneous washing and concentration of magnetic microparticles was demonstrated using a rotational magnetic system under a continuous-flow condition. The rotation of periodically arranged permanent magnets close to a fluidic channel carrying a suspension of magnetic particles allows the trapping and releasing of particles along the fluidic channel in a periodic manner. Each trapping and releasing event resembles one washing cycle in conventional biological assays. Concentration efficiencies of 99.75 +/- 0.083% at a flow rate of 200 A mu l/min and 88.10 A +/- 3.17% at a flow rate of 1,000 A mu l/min and a purification efficiency of 99.10 A +/- 4.3% at a flow rate of 900 A mu l/min were achieved.