The crossflow filtration of magnesium hydroxide slurries is described. The pseudo steady state flux is shown to correlate with the wall shear stress. A deposit of appreciable thickness builds up on the filter tube, and the correlation improves when the deposit thickness is included in the calculation of wall shear stress. A technique to deduce the deposit thickness from pressure measurement in a single filtering tube is described. The model has been tested using filter tubes with an uncoated diameter of 4 mm and 14 mm filtering non-Newtonian slurries with solids concentrations ranging from 13% to 24% by volume. For particles which can substantially penetrate a filter the wall shear stress model is shown not to apply, as the filter membrane is subject to internal blocking, which severely reduces the filtration rate.