The thermal degradation of aromatic polyimides in nitrogen at 700°C was studied using pyrolysis gas chromatography, infra red spectroscopy, and radiochemical techniques. Degradation medaanisms were postulated to account for the breakdown products found. Particular attention was paid to the ratio of CO2/C0 evolved during pyrolysis and this was found to vary with the moisture content of the polyimide and with the pyrolysis temperature.