In this study the effect of polymers was investigated on diffusional transport of model spherical particles (latex) of different size in an aqueous phase. Diffusion was monitored by dynamic light scattering (DLS) measurements. Solutions of carboxymethylcellulose (CMC Na) and polyvinylpyrrolidone (PVP) were used as models for two types of pharmaceutically relevant water-soluble polymers. Microviscosity effects could be observed only for the small sized particles in CMC Na solutions. In PVP solutions no microviscosity effects could be detected under the experimental conditions.