The influence of the cell resistance on the transient current signal after applying a potential step in condensation experiments has been investigated. The cell resistance was simulated by an external resistance in order to avoid chemical and double-layer effects. It could be shown that the shape of current transients depends sensitively on whether potentiostatic or nonpotentiostatic conditions exist on the surface during the phase transitions. For potentiostatic conditions four principally different current shapes could be detected in the system thymine/mercury, as was theoretically simulated with a model of coupled adsorption and condensation. The appearance of a single oscillation transient proved that the adsorption must be activation-controlled at least in a defined potential region, and commonly the supersaturation becomes time-dependent. Potentiostatic conditions are only fulfilled for small capacities and electrolyte concentrations higher than 0.1 mol/L on one hand and for relatively slow adsorption kinetics on the other. In the present case these conditions were fulfilled only for the mercury electrode. For higher capacities accompanied by faster adsorption kinetics, as is the case for gold electrodes with a diameter of 5 mm, the condensation takes place exclusively under nonpotentiostatic conditions. On gold electrodes in the physisorption region the simple interface model of a pure capacitor could not be applied. Probably additional reactions take place simultaneously with the adsorption process.