The present work is concerned with the study of the activation mechanism of Al in alloys produced by indium. The electrochemical behaviour of aluminium in NaCl solutions containing In3+ ions and the dissolution of Al-In and In-Al alloys were studied using potentiostatic, galvanostatic and potentiodynamic techniques, complemented by SEM. It was concluded that the aluminium activation is obtained only when indium comes into a true metallic contact with aluminium within an active pit and in the presence of chloride ions. Polarization curves for dissolution of Al-In and In-Al alloys were compared. The results suggest that the initial step in the dissolution mechanism of the Al-In alloy can be interpreted through chloride ion adsorption on a surface In-Al alloy. This adsorption occurs at more electronegative potentials than that of pure aluminium, thus avoiding repassivation.