The distribution of freely suspended particles in low Reynolds number, pressure-driven flow through bifurcations of microfluidic channels is measured experimentally. A bifurcation is a point where a channel splits into multiple channels. The partitioning of particles at microfluidic bifurcations differs from the partitioning of fluid, which can, in principle, be exploited to direct the particles along preferred paths in microfluidic devices or to prevent particles from entering certain microchannels. Experiments are conducted to examine effects of the angles between branches of the bifurcation and the microchannel cross-sectional shape on particle partitioning. Furthermore, effects of multiple bifurcations in series on the partitioning of particles also are examined. Under certain conditions, the particles can be completely segregated from the suspending fluid, which could be used as a flow-through filter for microfluidic devices. (c) 2005 American Institute of Chemical Engineers AIChE J, 52: 199-206, 2006.