In order to elucidate the property of water contained by the stereoic network in the vitreous gel, the conductivity of sodium hyaluronate solutions was measured in various concentrations at 25 degrees C and the relationship between concentrations of sodium hyaluronate and conductivity was evaluated. Each conductivity curve was divided into three stages. Equivalent conductivity was highly dependent upon the concentration of sodium hyaluronate at high and low concentrations, but was rather independent of it in intermediate concentrations. These results suggest that there are three types of water dependent upon the concentration of sodium hyaluronate, indicating physical variety, and that sodium hyaluronate solution in the intermediate concentration may possibly have a buffer homeostatic action on the ionic environment in the vitreous body.