Polysaccharide solids containing a large amount of water were used as a medium for conventional electrochemical measurements instead of liquid water. It was succeeded to prepare a tight and elastic solid by applying very carefully a microwave, when solubilizing the polysaccharide in water. It was successfully shown that the cyclic voltammogram (CV) of K4Ru(CN)(6) in the tight 2 wt.% agarose or carrageenan solid containing excess water was almost the same as in a liquid water. The apparent diffusion coefficients of the molecule (D-app) shows similar values in the solid as well as in a liquid water indicating that the complex can diffuse in the solid the same as in a liquid water. Similar results were also obtained for the redox molecules, K4Fe(CN)(6), methylviologen (MV2+) and Ru(bpy)(3)(2+), but for larger size molecules, on increasing their concentration, diffusion is suppressed showing a possible control of molecular diffusion by designing its size and the kind of the solid matrix including their concentrations. The electrochemical response of a modified electrode, in the present case prussian blue (PB)-coated electrode, could be measured in these solids the same as in liquid water indicating that the resistance between the PB film and the polysaccharide solid is almost the same as the interface between PB and water. (C) 2004 Elsevier Ltd. All rights reserved.