The mechanical properties of PEEK 450G have been extensively investigated. The compressive properties were measured at strain rates between 1 X 10(-4) and 3000 s(-1) and temperatures between -85 and 200 degrees C. The tensile properties were measured between the strain rates of 2.7 x 10(-5) and 1.9 X 10(-2) s(-1) and at temperatures between -50 and 150 degrees C. The Taylor impact properties were investigated as a function of velocity and various large-strain compression tests were undertaken to explain the results. The fracture toughness was investigated as a function of temperature and compared with previous literature. Additionally, the fracture surfaces were studied by microscopy. As with all semicrystalline polymers the mechanical response is a strong function of the strain rate and testing temperature. A previously reported phenomenon of darkening observed in Taylor impacted samples is shown to be due to reduced crystallinity brought about by large compressive strain. For samples deformed to large compressive strains using a variety of techniques and strain-rates the measured Vickers hardness was found to decrease in accordance with reduced crystallinity measured by other techniques. (c) 2006 Elsevier Ltd. All rights reserved.