Cake filtration, often referred to as dead-end filtration is used to separate microbial solids from aqueous solutions. In order to scale up such processes, it is necessary to determine the specific resistance and compressibility of the microbial cell cakes. Equations obtained from conventional cake filtration theory must be applied with particular care in such situations with due regard to the assumptions made in deriving them. This communication is intended to present a brief account of the conventional theory and to provide an examination of the filtration flux equation and the conditions under which this equation may or may not be used. Methods to obtain specific filtration resistance from water permeation through formed filter cakes must account for the concentration profiles within these cakes and the fact that they may not correspond to those obtained during a conventional filtration process. (C) 2008 Elsevier B.V. All rights reserved.