The relationship between the pore liquid pressure (p(L)) and the cake compressive stress (p(s)) is required in analyzing cake filtration. This relationship (for the one-dimensional case) is commonly assumed to be d(PL) + d(Ps) = 0 although similar but different ones may also be advanced from the multiphase flow theory. The effect of these different expressions is studied by examining the correspondence between cake filtration data and the compression-permeation cell measurements of two specific systems.