The curing and structure of an epoxy system containing dicyandiamide (DICY) as hardener were studied as a function of temperature and the presence or absence of copper with the use of differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy in photoacoustic mode (FTIR-PAS). Spectroscopic analysis of specimens taken from the DSC helped to clarify the reaction mechanism in terms of the different schemes that have been proposed. The initial stages, corresponding to the first peak in the DSC exotherm, involve the usual epoxide-amine reactions closely followed by a reaction between DICY nitrile groups and hydroxyl groups to form structures containing iminoether and urea groups. These reactions are slightly retarded in the presence of copper. At higher temperatures, corresponding to the second peak in the exotherm, these structures are transformed into others believed to contain urethane ester groups. This reaction, which may be considered to constitute a form of degradation, is significantly accelerated in the presence of copper. The effect is particularly large around 180 degrees C, a temperature commonly used to cure such systems, so the results have important practical implications, for example, in the lamination of circuit boards. (C) 2000 Government of Canada. Exclusive worldwide publication rights in the article have been transferred to John Wiley & Sons, Inc.