The influence of long-term ambient storage conditions in the presence of air has been examined on the thermal and photooxidation of unstabilized polypropylene. Samples of polypropylene have been aged under ambient storage for 12 years together with a control sample kept under refrigeration at -20 degrees C. The samples have been examined using second order-derivative absorption, fluorescence and phosphorescence spectroscopic techniques, thermal analysis (d.s.c.), light scattering and hydroperoxide analysis. All the polymer samples stored under ambient conditions exhibit significant increases in luminescent species and hydroperoxide concentrations as a consequence of slow oxidation processes. The d.s.c. and light scattering analysis show that these polymers exhibit an increase in crystallinity compared with that which has been stored by refrigeration. The data are related to the thermal and photooxidative behaviour of the polymers using Fourier transform infra-red spectroscopy (FTi.r.) and compared with that of a modern suspension grade polypropylene.