Potential, pH, and their gradients are important parameters in determining the electrochemical reactivity of metals in crevices. Although a potential drop alone within crevices can be responsible for the activation of crevice corrosion, changes in pH may be necessary for crevice corrosion to occur. In cases where acidification forms an active peak in the polarization curve, pH and potential play synergistic roles in determining the onset of crevice corrosion. This synergistic relationship is explored by measuring gradients in pH and potential within crevices during the induction period preceding crevice corrosion. Crevice corrosion was found to initiate due to the potential drop in the crevice into an active peak in the polarization curve formed by acidification.