A suspension of rigid noninteracting spheres in a Newtonian medium is structurally the simplest system which might exhibit such colloid-rheological phenomena as steep increase of viscosity with concentration, non-Newtonian and time-dependent thixotropic effects, and turbulence at anomalously low Reynolds numbers. A complete theory must include the dependent of the viscosity upon eight dimensional quantities, all of which happen to be experimentally variable and measurable. Dimensional analysis shows the reduced viscosity to be a function of five dimensionless groups, one of which governs non-Newtonian behavior, another the time-dependent thixotropy. A third group has the structure of an internal Reynolds number, hence may play a role in anomalous turbulence and dilatancy. The possibility of extending the dimensional approach to systems of more complex structure is discussed.