The effect of stereoregularity on the thermo-oxidative degradation of poly(propylene)s, isotactic (IPP) and syndiotactic (SPP), was compared with that of high density polyethylene (HDPE) by means of chemiluminescence (CL). SPP is extremely stable to thermal oxidation and CL signals appeared much later than in IPP and even later than in HDPE. For example, at 160 degrees C the maximum intensity of CL was measured after only 13 min for IPP, 60 min for HDPE and 260 min for SPP. IR spectroscopic results support the conclusions drawn from CL results.