Solid motion can be classified into translational motion and rotational motion; both play an important role in a wide range of engineering processes. While translational motion has been extensively studied in various systems, there is a lack of information on rotational motion, possibly due to a lack of appropriate experimental techniques. For a number of mixing processes involving heat transfer for solid-liquid mixtures, the heat transfer coefficient between solid and liquid is critical in determining process times and overall product characteristics, and is greatly dependent on both rotational and translational behaviours of the solids, which ideally need to be studied simultaneously. This paper presents a new technique, Multiple-Positron Emission Particle Tracking (Multiple-PEPT), which can follow multiple particles simultaneously through a considerable thickness of surrounding material. Both translational and rotational motions of the solid can be reconstructed. The accuracy of the method for the translational velocity was better than 10% while for the angular velocity 23% for speeds up to 0.25 m/s. Multiple-PEPT will therefore offer the possibility to study translational and rotational motions for a range of engineering systems. The potential applications of tracking solid translational and rotational motions are illustrated by an example of tracking a cubed potato in a rotating can. (C) 2008 Elsevier Ltd. All rights reserved.