This paper deals with the effect of different low-molecular-weight poly(ethylene oxide)s on the rheology of concentrated aqueous colloidal silica suspensions (volume fraction >0.2) with the aim of obtaining well-dispersed media. Results are correlated with the physico-chemical characteristics of the systems that govern the ranges of the various operating interactions, i.e., mainly surface coverage, molecular weight of the polymer, and ionic strength of the medium. Optimization of the fluidification occurs to be strongly linked to these parameters. An unexpected effect of free polymer bulk concentration leads to improved fluidification when the characteristic lengths of the system are correctly adjusted; it has been interpreted in the frame of recent theories. Copyright 2000 Academic Press.