Experiments designed to study the relationship between the hydraulic conductivity and the water content of a porous body were performed on two inert porous materials packed in long columns. The experimental results obtained are presented. They show that the relationship is hysteretic and that the repeated variation of the water content between any two limiting values results in a closed hysteretic loop. The relationship is subsequently examined in the light of the domain theory. It is found that the distribution functionHfor the conductivity elements may be considered as independent of the water contentsrVdandrVwat which the increment of water content reverses from negative to positive and from positive to negative, respectively, and therefore that the conductivity elements may be considered as independent. Distribution diagrams are obtained from an analysis of the primary depletion curves according to the independent domain concept. The hysteretic paths calculated by means of these diagrams show satisfactory agreement with the experimental paths.