The problems related to tortuosity variation whenever filter cakes are composed of cells with different shapes and compressible biosuspensions are discussed. Presented examples show that neglecting the tortuosity variation may lead to significant miscalculations of cake porosity or of specific cake resistance. Specific cake resistance of rod-like particles in cross-flow filtration depends on the higher tortuosity obtained by the shear-induced ordered arrangement. In turn, spheroid cells such as baker's yeast cells do not affect tortuosity as much as the rod-shaped cells. By including tortuosity as a parameter of compressible cakes, a more precise representation of cakes' behaviour may be obtained. The tortuosity becomes a highly significant parameter with the increase in filtration pressure. (C) 2002 Elsevier Science B.V. All rights reserved.