A description is given of the determination of the impact energy of concrete reinforced with discontinuous fibres of steel or twisted fibrillated polypropylene film. The design and instrumentation of a Charpy type of pendulum impact test machine is outlined, the machine being capable of completely fracturing in a single blow fibre concrete beams measuring 100 x 100 x 500 mm. This, machine was used to determine the energy absorbed in the fracture process both from the amplitude of the pendulum swing and also from the record of force developed on the pendulum head during the impact. The latter method enabled the energy absorption to be determined with respect to the central deflection of the test beam in a manner analogous to energy determination from the area under a conventional slow-rate load-deflection curve. A variety of steel fibre types and two lengths of chopped fibrillated polypropylene film fibre were used to produce composites with two fibre volume fractions and these were tested at two ages. As well as being tested in impact, most of the fibre concrete types were failed in flexure at a conventional slow rate of loading and the energy absorption was determined from the area under the load deflection curve. The high work of fracture of these materials relative to plain concrete is quantified and it is shown by comparison of the energies at given deflections in slow and in fast loading, that the work of fracture is not particularly rate sensitive. The implications of this conclusion with respect to the standardisation of test methods for toughness measurements on fibre concretes are assessed.