This paper reports results on the interaction of CO with Pt(s)[n(111) x (111)] electrodes in perchloric acid medium. Charge displacement experiments allow the estimation of the potential of zero total charge (pztc) values for this series of stepped surfaces. The pztc values decrease linearly with the step density for n greater than or equal to 5, while for shorter terraces a plateau is observed. Knowledge of the pztc is a key point in the evaluation of the CO coverage by means of coulometric measurements. Using this method. we have calculated the CO surface concentration at saturation for a series of stepped surfaces. The resulting values are similar regardless of the step density, but they are significantly lower than those for the Pt(111) basal plane.