The thermal degradation of poly(1,4-phenylene ether-sulfone) (PES), Mw 47 000, and of a polysulfone resin (PSR) Mw 75 000, was studied by flash-pyrolysis, with a temperature rise time (TRT) of 8 ms. Pyrolysis products were monitored by a pyrolysis-gas chromatography flame ionisation detector/flame photometric detector (Py-GC-FID/FPD) and pyrolysis-gas chromatography mass spectrometry (Py-GC/MS). Special attention was given to the formation of sulphur-containing pyrolysis products. The kinetics of SO, formation were studied by sequential pyrolysis of PES and PSR. It was possible to differentiate between the rates of formation of SO2 from PES and PSR. The rate of formation of SO2 was somewhat higher for PES than for PSR. The activation energies were 270 and 280 kJ/mol, respectively, and the frequency factors were 10(14) and 10(15) s(-1).