The reduction process of inosine on a mercury electrode has been studied by differential pulse polarography (DPP), elimination polarography (EP), and potentiostatic macroelectrolysis. The measurable reduction signal of inosine can give only DPP and EP and can be measured only in the pH range between 1.4 and 2.5. For pH values below this limit the hydrogen evolution makes the measurement irreproducible, while for pH values above this limit the hydrogen reduction current totally overlaps the inosine signal. The elimination of the charging and kinetic current with the conservation of the diffusion current by EP application revealed the inosine reduction wave. The concentration dependence of this wave indicates the inosine association resembling the micelle formation or phase transition with a critical concentration around 0.1 mM. The EP wave corresponds to the reduction of inosine monomer. The DPP peak appears in more negative potentials than the EP wave and corresponds to catalytic hydrogen reduction. The reduction scheme for inosine monomer based on the results of EP and of the analysis of macroelectrolysis reduction products leads to a reduction scheme with four electrons and four protons and with the breaking of the pyrimidine ring. The inosine associates, inosine and the inosine reduction product are responsible for the hydrogen reduction catalysis. The process in the associates occurs by the recombination of hydrogen atoms travelling along the train of stacked hypoxanthine molecules in one associate. With respect to the known similarity of the reaction processes of purine derivatives, the present study can serve as a base for the interpretation of their electrochemical behavior.