Sodium benzoate and benzotriazole, separately and together, are investigated as corrosion inhibitors for grey cast iron. Good inhibition can be obtained when both are present in con-centrations of around 1%; either compound separately is less effective, suggesting a synergistic effect. The same holds for machined surfaces. Use of one compound, with modification of the pH (to approximate the effect of the other), gives poorer inhibition than use of both compounds in the above-mentioned concentrations. A similar synergistic effect for the corro-sion inhibition of an aluminum alloy may exist; mechanisms to account for the effect are considered briefly. -- AATA