Associating polymers are hydrophilic long-chain molecules containing a small amount of hydrophobic groups (hydrophobes), and behave as flocculants in aqueous suspensions. The effects of associating and nonassociating polymers with molecular weights of about 2.5 X 10(4) on the theological behavior are studied for silica, latex, and mixed suspensions. Because the hydrophobes adsorb onto hydrophobic surfaces and water-soluble chains onto hydrophilic surfaces, two single suspensions are highly flocculated by a bridging mechanism. The complex suspensions which are prepared by mixing the silica and latex suspensions with the associating polymer at the same concentration show a drastic reduction in viscosity. Since the long chains of associating polymer attach to the surface at many points, the adsorption onto silica surfaces is dominant in the complex suspensions. The hydrophobes extending from the chains adsorbed onto silica particles can adsorb onto latex particles. The associating polymer acts as a binder and the hetero-flocculation between silica and latex is induced. The formation of composite particles in which the silica particles are covered with latex particles is primarily responsible for the drastic decrease in viscosity. (c) 2006 The Society of Rheology.