Swarm theory for flow through a system of fibers is combined with trajectory calculations for colloidal particles to predict single-pass retention efficiencies. Streamlines and particle trajectories determined from swarm theory are compared with results obtained using other hydrodynamic models to assess the sensitivity of predicted efficiencies with respect to the type of flow model used. Brownian motion contributions to retention are determined by adapting existing convective diffusion theory to the flow fields under consideration. Results of a parametric study are presented to elucidate the effects of the hydrodynamic and surface and colloid variables on retention. Predicted efficiencies are compared with experimental data for TiO 2 particles depositing on nylon fibers and with an alternate theory based on convective diffusion calculations.