The effects of the sulphate ions and the pH on the strength of concrete and reinforcement steel have been investigated. Concrete and reinforced concrete samples prepared by using mixing water having different sulphate ion concentrations (standard, 400 ppm and 3500 ppm) were cured in a water bath containing the same ion concentrations of mixing water or distilled water at two different pH values (8 and 5). The samples were exposed to the environments for 90 days. The compressive strength of concrete, pH values of bath, galvanic current changes and potentials (vs. Ag/AgCl) of reinforcing steel were measured. It was observed that the compressive strength of the concrete decreases as the SO4= ion concentration increases. The galvanic currents were high for the first 28 days and then these currents decreased steadily. It was found that the potentials have been rising up to the passive potential of the reinforcing steel where the SO4= concentration is low. (C) 1997 Elsevier Science Ltd.