Measurement of the passivating current from titanium microelectrodes in acidic chloride solution shows that the passive surface undergoes transient microscopic breakdown. Such breakdown occurs well below the pitting potential. The observed events are thought to be due to the nucleation of corrosion pits; very few of these show evidence of propagation, and there is no permanent propagation. The frequency at which these breakdown events occur is low, and the process persists for a long time.