Nonmagnetic microparticles (e.g., cells, polymer beads) immersed in a magnetic fluid (ferrofluid) under a nonuniform magnetic field experience a magnetophoretic force in the direction of decreasing magnetic field strength. This phenomenon was exploited in the development of a continuous magnetophoretic countercurrent separation for the removal and concentration of micron-sized particles from aqueous suspensions, and in particular as a viable approach for cell clarification of raw fermentation broth. A magnetic fluid is added to the cell suspension, the mixture is introduced to the magnetic separator, which consists of an open flow tube passing between pairs of magnets that move in a direction counter to the flow of the suspension. The cells are pushed ahead of the magnet pairs owing to the magnetophoretic forces acting on them, collected in a tube upstream of the feed injection point, and removed as a concentrated suspension for further treatment. (C) 2011 American Institute of Chemical Engineers Biotechnol. Prog., 27: 744-750, 2011