Solutions containing high molecular weight hyaluronate at concentrations around 10 mg/ml exhibit interesting rheological properties due to formation of a highly entangled network of flexible polysaccharide molecules. We have performed an extensive study of the rheological properties of hyaluronate solutions as a function of concentration and molecular weight. In this paper we review some basic rheological concepts, and discuss the rheological properties of hyaluronate solutions at high concentrations and medium to high molecular weights (1-5 million). The bulk viscosity (zero shear viscosity) of hyaluronate solutions is strongly dependent both on concentration and molecular weight. A 2-fold increase in concentration or molecular weight results in a 10-fold increase in bulk viscosity. For application in body compartments, the concentration of hyaluronate cannot be increased much above 10 mg/ml due to the highly non-ideal colloid osmotic behaviour of hyaluronate. High viscosity hyaluronate solutions must therefore be based on high molecular weight material.