Thermal and UV oxidative degradation of poly(acrylonitrile-butadiene-styrene) (ABS) containing a hindered amine stabilizer (HAS) was studied by electron spin resonance (ESR) spectroscopy and ESR imaging (ESRI). The imaging technique allowed digital (nondestructive) spectral profiling of the HAS-derived nitroxide radicals: Their intensity profile was determined by 1D ESRI, and the spatial variation of the ESR line shapes was determined by 2D spectral-spatial ESRI. The UV light was provided by fluorescent lamps with maximum intensity in the range 290-320 nm (UVB) or by a Xe are that closely resembled the solar spectrum. Upon UVB irradiation the nitroxide signal was initially strong only on the irradiated side and increased with time through the sample. These results were taken as evidence for extensive damage on the irradiated side and slower thermal degradation in the entire sample. The effect of UVB radiation was in marked contrast with that of a Xe source; after Xe irradiation the nitroxide radicals were detected at both the irradiated side and the opposite side, and their intensity was negligible in the sample interior. Spatial variation of the ESR line shapes was observed for irradiation with both UV sources. The spatial distribution of the nitroxide radicals was, however, homogeneous during thermal degradation at 318 and 333 K, and there was no spatial variation of the ESR line shapes. The results allowed mapping of the line shape and intensity of nitroxide radicals within the sample as a function of treatment time and provided mechanistic details on the early stages of the degradation process. This study suggested a hierarchical variation of the HAS-derived nitroxide concentration: within morphological domains in ABS on the scale of a few micrometers and within the sample depth on the scale of millimeters.