The volume fraction (holdup) of mica and graphite in water slurries has been determined in a continuously operating column (10 cm in diameter and 447 cm in height), using an electrical conductivity-based method. The results were checked against those given by a pressure method and the actual volume fraction of solids determined by an isolating technique. The shape of the dispersed particles significantly affected the conductivity of the dispersion. Neither Maxwell＇s (1892) nor Bruggeman＇s (1935) model yielded acceptable estimates of holdup. Fricke＇s (1924) model, which takes the shape of the particles into account, adequately predicted solids holdup (5-12% v/v in this case). The required shape factor for Fricke＇s model was obtained by SEM analysis of several particles. In the case of graphite, an estimation of particle conductivity was required which was obtained by back-calculation. The observations are of relevance in flotation systems where conductivity is being considered for on-line phase holdup determination.