The viscoelastic properties of dispersions of microcrystalline boehmite (AlOOH) particles, covering a range of high concentrations (>10% w/w) and containing different electrolytes, have been measured under oscillatory shear with a Weissenberg rheogoniometer. Stable dispersions were highly elastic and often thixotropic—properties which are ascribed to short range (3 –, BrO3–, F–, SO42–) this elasticity was lost and plastic properties developed. Interparticle repulsion is attributed to extensively solvated polynuclear aluminium cations, formed at the boehmite surface during acid peptisation, whose presence was consistent with quasielastic neutron scattering and other evidence. Light scattering measurements on dilute dispersions ( 0.1) a stable and coherent structure analogous to the individual aggregates is proposed.