The paper describes a study undertaken to examine a methodology to determine the rate and severity of chloride-induced corrosion of steel embedded in concrete using the half-cell potential test. Preliminary studies undertaken in the laboratory, using a wide range of concrete variables, indicated that an effective relationship between half-cell potential (Ecorr) and corrosion current (Icorr), from polarisation resistance measurements, did indeed exist. The study was subsequently extended to an external marine environment where sections of full-scale beam, slab and column elements were exposed to seawater attack for a period of 5 years. By instrumenting these elements prior to exposure, it has been possible to demonstrate that by establishing a local relationship between Ecorr and Icorr, the extent of corrosion damage can be reasonably estimated over the full section. The practical implications of this and a proposed test procedure are discussed.