Results are presented from a study of the performance of reinforced concrete in a marine environment. Reinforced concrete specimens from three series of concrete mixes of nominal strength grades C25, C35 and C45 and with a range of PFA levels (0–50%) were placed in the tidal zone of the BRE marine exposure site. Measurements of reinforcement weight loss and chloride ion penetration were carried out on the specimens after two years' exposure. The results indicate that chloride ion penetration during early exposure is controlled by sorptivity rather than diffusion, and predictions of diffusion coefficients derived from chloride concentration profiles are not valid. No significant increase in the chloride content at depths below 10 mm were observed between one and two years for concretes containing 30% or more PFA, whereas substantial increases were observed for the OPC control concretes. The PFA concretes were far more resistant to the penetration of chloride ions than the OPC concretes and consequently corrosion of steel reinforcement was reduced in the PFA concrete. It is concluded from results to two years that in marine conditions PFA concrete provides much improved protection to steel reinforcement, compared with OPC concrete of equal strength grade, cementitious content (OPC + PFA) or water–cementitious ratio. Further assessments will be carried out after 5 and 10 years exposure. These results are discussed in the context of current specifications for concrete exposed to marine conditions.