ABS is a well-known and widely used rigid engineering polymer. The mechanical properties of ABS are critical to its proper functioning in a given application, such as a medical device. It is therefore important to retain those properties during processing, fabrication, and use. To that end, thermal analysis and mechanical testing were employed to understand the origin of observed mechanical property losses. Oxidation onset temperature (OOT) testing and differential scanning calorimetry (DSC) analysis indicate a slightly lower onset temperature and a higher glass transition temperature, respectively, for parts which demonstrate a reduction in mechanical properties. It is also demonstrated that degradation of the butadiene-phase of the ABS is responsible for the mechanical property reduction, and that this degradation only proceeds at an appreciable rate at elevated temperatures in the presence of oxygen. (c) 2006 Published by Elsevier B.V.