We studied the TiO 2 pigment distribution along cross sections of injected isotactic polypropylene samples after they were aged by light exposure for 515 and 3000 h in accelerated test equipment. The TiO 2 pigment distribution was studied so that we could understand the whitening process occurring in this type of plastic. For these studies, we used a 20-m X-ray microbeam from a synchrotron light source. We observed that the aged and nonaged samples had almost homogeneous distributions of Ti in the cross sections; therefore, pigment migration could not have been responsible for the surface whitening process. There were maxima of Ti intensities that were not in the same region for all samples. This behavior could be explained by the heterogeneity of the extrusion and injection-molding processes.