Positron emission particle tracking, generally known as PEPT, is an imaging method for following the motion of a single tracer particle in a dense medium; this particle may be as small as 100 mum. The imaging method has been applied to many operations, among these being the mixing of dry powders and granular materials. There is one class of equipment in which mixing is imparted by the use of blades that has much in common with equipment used for agglomeration. From studies on dry mixing, it is possible to deduce some of the mechanisms governing behaviour and a physically based approach to design and operation is now becoming possible. Little is presently known from applying PEPT to agglomeration. However, PEPT will be of direct value in deter-mining the occupancy of material in equipment as a function of position and time; it will provide similar information on the velocity field. It is capable of development for use on commercial scale agglomerators. While it does not allow direct observation of the collision processes that are critical for growth and breakage, PEPT does provide a quantitative basis from which logical inferences are possible. (C) 2004 Elsevier B.V. All rights reserved.