The corrosion of glass fibres in acid solution is well known and is thought to be responsible for many instances of failure in glass reinforced plastic materials. Although it is generally accepted that cations are leached from the glass matrix into the acid solution, the precise chemical mechanism and rates of corrosion are still not fully understood. For example, it is not simply the hydrogen ion concentration of the corroding medium that affects the rate of corrosion, but in many cases the anion associated with the acid plays a major role. Anions that can form insoluble salts or complexes with cations in the glass matrix can increase the rate of leaching and hence accelerate the corrosion process. In the case of hydrochloric acid, it has been suggested that chloride anions form complexes with iron(III) ions leached from the glass and this in part increases the rate of corrosion. This paper investigates the corrosion rate of glass fibres exposed to hydrochloric acid at different concentrations and temperatures by measuring the residual strength of the fibres before and after exposure. The leaching rate of cations into solution is also measured using atomic absorption spectroscopy. As expected, increase in temperature increases the rate of corrosion and this can be modelled using a simple Arrhenius plot to determine the activation energy of the process. Strength retention and rates of leaching of individual cations are compared in an attempt to explain the mechanism of corrosion. (C) 2004 Kluwer Academic Publishers.