The dynamic rheological behavior of gelled Ludox suspensions in the presence of the structure-breaker ammonium counterion and the structure-maker sodium counterion has been investigated. Depending on the nature of the electrolyte and its concentration, the results highlight the crucial effect of the network microstructure on the theological results. Within the same microstructure, the strength of gelled networks has been found to be greater in the presence of the poorly hydrated ammonium counterions at any Ludox volume fraction. The obtained results were discussed with respect to recent contradictory trends reported in the literature concerning the behavior of silica suspensions. (C) 2004 Elsevier Inc. All rights reserved.