ABSTRACT--An automated 3D tracking technique for studying the motion of particles deep within the tumbling ball charge of an experimental grinding mill is described. The use of a Biplanar angioscope for the accurate location of objects moving in three dimensions is a novel application of this X-ray equipment. The X-ray beam used to produce the image data was parameterized using an accurately measured control frame. Preliminary experiments were conducted on a Perspex mill with a length and diameter of 140 mm. The digitally acquired X-ray images of the tumbling mill were processed using a fully automated imaging technique. The final 3D coordinates of the tracked particle trajectories are accurate to within 0.40 mm. This indicates that the technique is robust and thus capable of providing accurate verification data for the numerical modeling of the tumbling motion in mills.