The rejection coefficient of nonspherical particles from ultrafiltration and microfiltration membranes has been examined from both theoretical and experimental perspectives. Modeling efforts focused on incorporating the convective hindrance factor for a capsule shaped particle in a cylindrical pore into predictions of the rejection coefficient. First, the convective hindrance factor was approximated using previously reported results for the hydrodynamic resistances experienced by a sphere in a pore. Second, computational fluid dynamics calculations predicted the convective hindrance factor for a capsule in a cylindrical pore. Results from both approaches indicate that including hydrodynamic interactions in predictions of the rejection coefficient has a greater effect for smaller particles and particles with smaller aspect ratio (i.e., close to spherical shape). Rejections of several rod-shaped Gram negative bacteria with aspect ratio from 2 to 5 by clean track-etched membranes were in general agreement with theoretical predictions. (c) 2013 American Institute of Chemical Engineers AIChE J, 59: 3863-3873, 2013