The corrosion behaviour of aluminium in 1.0 mol l^–1 solutions of HCl, H₂SO₄, HNO₃ and HClO₄ has been investigated in the presence and absence of added Cl^– ions. The rate of corrosion of the metal in HCl and in acid solutions containing Cl^–, was significantly higher than in the other solutions studied and is attributed to Cl^– pitting. The rate of corrosion was found to be zero order overall with an observed rate constant dependence on Cl^– of the form (k_obs–k₀)=kK₂[Cl^–]²/(K₁[O₂]+K₂[Cl^–]) where K₁ and K₂ are, respectively, the equilibrium constants for O₂ and Cl^– adsorption on the metal surface. The addition of the sodium salts of N-n-butyl, N-ethyl and N-phenyl dithiocarbamates was found to have an accelerating effect on the corrosion rate, whereas the addition of the quadridentate macrocyclic amine cyclam (1,4,8,11-tetraazacyclotetradecane) and its open-chain analogue DND (3,7-diazanonane-1,9-diazine) was found to offer inhibition characteristics. These latter rates were investigated at 30, 35, 40, 45 and 50 °C in various amine concentrations. A mechanism involving three competitive equilibria, viz. molecular oxygen adsorption, Cl^– adsorption and inhibitor adsorption, followed by a rate-determining chloride ion catalysed dissociation step is proposed for the reaction. Finally, the pitting potentials of Al in aggressive acid solutions containing various Cl^– concentrations were determined from anodic polarization curves. These data were discussed and correlated to the overall mechanism of pitting corrosion.