Aggregation and agglomeration have been extensively reported in the literature during the prolonged milling of powders. This phase is usually considered non-productive and is delayed by the use of grinding aids. The agglomeration phase of sucrose, sodium chloride, lactose and paracetamol has been studied as a possible method of producing pharmaceutical granules. In this paper the mechanism of agglomeration at the particulate level is examined. It is shown, that following particle size reduction, there is agglomeration of the fine coherent particles into a loose granular structure. This granule is then either compressed into a harder granule or remilled to produce fine powder. Finally, an equilibrium between size reduction and agglomeration is attained. © 1979.