For the pharmaceutical industry, powder segregation can occur in many processes such as blending and compression solid dose unit operations. Yet it is important that the high quality standards of drug product manufacture are maintained throughout the whole processes. Powder segregation has been identified by the pharmaceutical industry as a potential issue, and in some cases it may cause variability in tablet assay and uniformity throughout a compression run. Early studies suggested for certain Direct Compression (DC) products, the separation of Active Pharmaceutical Ingredient (API) from excipients could arise due to air-induced segregation of the powders discharging from an Intermediate Bulk Container (IBC) to the tablet press via a vertical chute. Segregation tests were carried out on trial powder blend materials supplied by GlaxoSmithKline (GSK), using a laboratory-scale air elutriation test facility at The Wolfson Centre. Particle size analysis of the virgin and segregated sub-samples clearly indicated that powder segregation occurred as a result of aerodynamic effects. Subsequent chemical assay results concurred with the particle size results. Flowability testing of the powder blends indicated them to be free-flowing materials: this in addition to the presence of large particle size differentials within the powder blends is the likely cause of the susceptibility to air-induced segregation. (C) 2010 Elsevier B.V. All rights reserved.