Pit development on nickel and nickel-molybdenum alloys in 0.1 M NaCl + 0.05 M Na2SO4 solution under potentiostatic conditions was studied. When the molybdenum content of nickel-molybdenum alloys is above a threshold value, it has the effect of reducing the current flowing from the surface. Examination by scanning electron microscopy shows the presence of two distinct pit morphologies : terraced faceted pit surfaces resulting from crystallographic dissolution is observed on nickel, while shallow pits with smooth surfaces are formed on Ni-5Mo because of the presence of a salt film at the pit bottom. The experimental results were analyzed according to a model for pit growth. The results quantitatively correlate the conductivity of the pit electrolyte and the conductivity and thickness of the salt film with the dissolution df-metal within a pit.