A structural epoxy-based adhesive cured with dicyandiamide (DDA) and 4,4＇ diaminodiphenylsulphone (DDS) has been aged at elevated temperatures under various gaseous environments. Weight loss was accompanied by enrichment of oxygen, sulfur, and nitrogen, near the polymeric surface, after aging in oxygen containing atmospheres, as shown by X-ray analysis. Sulfur dioxide was detected in the aging environment. Results strongly suggest chain scission by thermolysis combined with thermo-oxidative degradation occurring near the exposed surface. (C) 2000 John Wiley & Sons, Inc.