The dynamic testing of high strength automotive steel grades is of great practical importance if their crash-worthiness is to be evaluated. During forming operations, steels are processed in a controlled dynamic manner. In collisions, the deformation is different in the sense that the deformation is not controlled, i.e both strain and strain rate are not pre-determined. No clear standard testing procedures are currently available to test high strength steels dynamically, in order to evaluate their performance during car crashes. High tensile strength TRIP-aided steels have been developed by the steel industry because of their promising high strain rate performance. The present contribution focuses on the effect of the strain rate and temperature on the mechanical behaviour of the low alloy high strength TRIP steel. The tests were carried out on the separated phases in order to determine their specific high strain rate deformation response. The temperature-dependence of the transformation rate of the retained austenite is presented. It is argued that the adiabatic conditions present during high strain rate deformations have a beneficial effect on the behaviour of TRIP steel. In terms of high strain rate behaviour, the high dynamic energy absorption performance of TRIP steels is now firmly established as they offer large dynamic energy absorption and homogeneous deformations for strain rates reaching up to 1500 per s. The properties of the low alloy TRIP steel are due to their multi-phase microstructure in which the combination of the high strain rate properties of the ferrite, bainite and retained austenite result in a 'composite' effect. The excellent high strain rate properties are mainly due to the strain and temperature dependence of the meta-stable retained austenite transformation to alpha' martensite. (6th Mesomechanics Conf., Internat. Conf. on Multiscaling in Applied Sci. and Emerging Technol. Fundamentals and Applications, Univ. of Patras, Patras, GR, May 31 - June 4, 2004)