Using the exact theoretical equations derived to describe the response in single-step chronocoulometry (SSC) and a reported method for correction of the double layer charge, the chronocoulometric response of the Cd(II) + KBr(1 M)/Cd(Hg) system is analyzed. The applicability of our theoretical equations and the quantitative use of the chronocoulometric technique are demonstrated. The potential step starts in the pre-faradaic potential range and ends at some potential inside the d.c. polarographic wave. From the charge response obtained with steps ending at the limiting current plateau, the value of the reactant surface excess corrected for double layer charging, was calculated. A detailed analysis of the dependence on the electrical variable sigma(m) of the reactant surface excess led us to propose a plausible adsorption isotherm to which both the Cd(II)-complex species and the bromide anion adsorbed on the electrode contribute.