Particle interactions in the discrete element method (DEM) are characterized by parameters that are often fitted or estimated due to the lack of accurate experimental measurements. This work reports on experimental measurement of the necessary interaction properties required for the DEM analysis, and on testing the DEM against the measured experimental results. The experiment is based on the in-flight binary collision of two spheres, monitored using digital photographic equipment. The coefficients of tangential and normal restitution and friction angles are derived. Preliminary numerical simulations using the standard viscous damping model are performed using the DEM and a comparison between experimental and numerical results presented. It is shown that the match is not good, indicating that the prediction of energy transfer at collisions will be incorrect. It is proposed that different contact models should be tested, to assess if the predictions improve. It is postulated that it may not be necessary to utilise the Hertzian theory of impact to derive the contact parameters, but rather be more accurate for DEM modelling to directly fit the parameters based on the controlled binary collision experiment. (c) 2005 Elsevier Ltd. All rights reserved.