The Paper describes a study undertaken to determine the effect of PFA on reinforcement corrosion due to chlorides in concrete. The results indicate that the time to corrosion initiation when PFA is included is greatly increased, but that the quantity of chlorides causing this does not differ significantly between PFA and OPC concretes. After a given period of exposure, the concentration of chlorides at the surface of the reinforcement and the resulting corrosion intensity were lower in PFA concrete. A relationship between corrosion rate, water-soluble chloride content and coeficient of chloride diffusion has been developed, suggesting that the ability of the binder system to limit chloride migration is an important factor influencing the corrosion process. From this a means is proposed of evaluating corrosion risk in concrete under chloride attack.