Аннотация:The question of the concentration variable in the theory of slow discharge (TSD) has been considered theoretically. The fundamental equations of the theory of slow discharge not restricted by an assumption that the values of the activity coefficients of the reactants in the bulk of the solution and in the adsorption layer are proportional (or equal) have been obtained and analyzed. It is concluded that under the conditions of low coverages of the electrode surface with the electrolyte components the rates of the discharge and ionization steps should be proportional to the bulk activities of the reactants. This conclusion is confirmed by the results of an investigation of the electroevolution of H//2 on an Hg electrode from acidified salt solutions.