Self-diffusion coefficients of Na+, <(D)over bar (i)>, inside hydrous stannic oxide have been measured in aqueous and alcoholic solutions at different Na+-capacities. <(D)over bar (i)> always displays the usual decrease with capacity, which seems to be much less profound at the relatively high capacities. There is apparently almost no effect of addition of methanol on <(D)over bar (i)>, whereas a decrease of <(D)over bar (i)>, which disappears towards relatively high capacities, occurs on addition of propan-1-ol. These results are in marked difference with previous results of the effective diffusion coefficients of Na+/H+ systems. This difference seems to indicate that the effect of alcohol addition in increasing the strength of electrostatic interaction of counter ions with the exchanger surface (a factor which, when predominating, decreases mobility) is higher with protons than with the Na+ ions.