Commercial fluorine production is conducted from KF.2HF melts at 85 degrees C in Monel cells that are subject to corrosion. Here we report studies of passivation and depassivation of the Monel in relation to that of Ni, its principal (65 wt %) constituent, by means of cyclic voltammetry and recording of open-circuit potential-relaxation transients. The latter exhibit arrests at characteristic Flade-type potentials and lead to information on the kinetics of passive film breakdown. The role of diffusion processes in such breakdown and him dissolution is evaluated using the rotating disc electrode technique which enables comparisons to be made with the passivation behaviour of the separate main components of Monel, viz. Ni and Cu.