The dependence of the pitting potential E-p of aluminium on chlorine ion concentration, chromate concentration, pH, and solution temperature was studied by a potentiodynamic method. It was found that E-p depends on the logarithmic concentration of the aggressive ion and the inhibitor, changes linearly with temperature, and is almost independent of pH. Considering the individual effects of these variables, a mathematical model that correlates the pitting potential with simultaneous variations of chloride and chromate ion concentrations and temperature is proposed. Model parameters were found by the use of experimental data. The resultant expression is E-p = 83.1 - 3.0T - 897.3 log[Cl-] + 865.7 log[CrO42-] + 2.7T log[Cl-] - 2.3T log[CrO42-] where E-p is expressed in millivolts, temperature T in kelvin, and chlorine ion concentration and chromate ion concentration in parts per million.