The thermal stability and trace volatiles content of polymers can be determined rapidly and conveniently by using a hot-filament pyrolyzer for heating the sample. The filament unit, of a type employed for pyrolysis-GLC analysis, consists of a platinum coil with an attached platinum/platinum–rhodium thermocouple for measuring the sample temperature. As the sample is heated the volatile products are monitored directly with a flame ionization detector, a dual recorder being used to chart both temperature and volatiles yield. At any stage of heating the products are analyzed, if desired, with a suitable GLC column. Thermal stability measurements of several polymers were generally consistent with results by conventional thermogravimetric analysis. Advantages of the method are high sensitivity for detection of low decomposition rates, speed of the temperature adjustment, simplicity of the apparatus, and small sample requirement.