Solid-polymer-electrolyte electrolysis was performed in electrolyte solutions of different concentrations. The higher the electrolyte concentration, the higher the concentration of dissolved hydrogen as H-2 molecule. The concentration of dissolved hydrogen was high in the high electrolyte solutions only when current density was high. In an effort to clarify this finding, the electrolytic generated hydrogen bubble was visualized using a high speed camera. Numerous bubbles were formed under high current density, therefore, the degree of bubble coalescence increased. The bubble coalescence, however, was inhibited by addition of electrolytes. In the electrolyte solution, the hydrogen bubbles maintained the released bubble size. The high concentration of dissolved hydrogen was attributable to the bubble coalescence inhibited by the electrolyte. (C) 2005 Elsevier Ltd. All rights reserved.