The topic of nanodielectrics is one that has grown enormously in importance since Lewis first introduced the concept of a nanodielectric in 1994. However, while nanodielectrics exhibit great promise, changes in macroscopic physical properties are determined by dispersion, and therefore it is imperative that reliable methods are available for the cost-effective determination of the dispersion state of the nanofiller in the host polymeric matrix. This paper details an investigation into the rheological response of PEO / montmorillonite (MMT) nanocomposites; MMT is a polar material and is therefore relatively compatible with aqueous systems. Three molecular weight PEOs were used - 100,000 g mol-1, 400,000 g mol-1 and 1,000,000 g mol-1. The rheological behaviour of a range of systems containing various levels of MMT were then studied, with the twin objectives of (a) producing materials with different shear histories and different degrees of MMT dispersion for study as described elsewhere  and (b) to explore rheological response as a practical means of determining the dispersion state of a nanofiller in a liquid polymer. This would have great practical utility as a quality control device in, for example, the production of epoxy-based nanodielectrics. In this paper we concentrate on the latter aspect of the work and describe the effect of polymer molar mass, polymer concentration, imposed shear history and nanofiller loading level on the rheological behaviour of the system.