The ability to predict rheological behavior of clay dispersions would be useful in formulating systems theologically modified by clays as well as designing equipment to handle clay based materials. Deriving predictive equations for these materials has been hindered due to the various mechanisms by which clay systems develop microstructure. This work seeks to observe the relationship between the yield stress, tau gamma, and the zeta potential, zeta, and determine the nature of the particle interactions for dispersions of laponite (a synthetic clay) and dispersions of a mixture of naturally occurring kaolinites and bentonites. It is found that the relationship of tau gamma to zeta(2) for clay suspensions is opposite to that found for homogeneously charged spheroidal colloids. This result can be traced to the type of particle interactions occurring, which for the systems studied appear to be edge-to-face attractions. (c) 2005 Elsevier Inc. All rights reserved.