Benzyl dimethyl-n-hexadecylammonium chloride (BHDC) was investigated for its effectiveness as a corrosion inhibitor of pure iron in carbon dioxide saturated 3% sodium chloride solutions. Both a.c. impedance and d.c. electrochemical techniques were used. The compound inhibited the anodic reaction and was effective at low temperatures. Data obtained fitted the Frumkin adsorption isotherm. The inhibition characteristics are interpreted in terms of thermodynamics and the structure of the compound.