Pitting in chloride solutions of 1000-2000 Å thick films of Al evaporated onto quartz substrates was studied. The anodic dissolution and hydrogen evolution current densities in the pit were both constant with time. The anodic current density and the pit morphology were, however, dependent on the pit growth potential. At low potentials, the pit current density increased linearly with potential, the pit surface was extremely rough, and pit growth was determined to be under ohmic control. At higher potentials, the pit current density was independent of potential and the pits became round and smooth, indicating that mass transport was rate limiting. © 1990.