Dilute suspensions of neutrally buoyant, uniform-diameter spheres in a viscous liquid are sampled through pores in the wall of a stirred tank. These studies are performed to investigate screening effects near the sampling orifice that cause samples to be deficient in solids. The ratio of sphere concentration in the sample to that of the original suspension ranges from 0.08 to 1.12. Sample concentration decreases with decreasing sampling pore diameter and increasing stirring rates. The objectives of this work are both to obtain experimental relationships and to develop predictive techniques relating flow fields to sample concentration. Sample concentration is predicted by calculating particle trajectories in the region near the pore and by accounting for steric exclusion. Particle trajectories can differ from fluid streamlines due to lift forces generated in the flow field. These estimates constitute a priori predictions, since they do not rely on or introduce any empirical parameters. Predicted values of sample concentrations agree closely with data.