An on-line thermogravimetry/gas chromatography/mass spectrometry (TG/GC/MS) system has been constructed through additions to and appropriate modifications of commercially available instruments. The system employed a Du Pont 951 thermogravimetric analyzer coupled to a Hewlett-Packard 5890 gas chromatograph/5970 mass selective detector system. A nickel tube, inserted directly into the area immediately above the TG sample pan, acted as a transfer line. An adsorbent trap with a heater and a heated six-way valve was installed between the TG and the GC. The volatile compounds generated from selected materials in the TG were adsorbed by the trap. After the heating and purging process, the trap was rapidly heated and the volatile compounds in the trap were swept into the GC injector and were then analyzed by GC/MS. The on-line TG/GC/MS system was examined by using selected natural products. A number of volatile compounds were generated from the samples by TG, separated by GC and identified by MS. The stability, the weight loss, and the evolution of compounds from the materials could be analyzed and studied.