The use of carbon powder to remove impurities can result in difficult and time-consuming charging and cleaning procedures due to the dusty nature of the carbon. In this paper the use of flow-through carbon cartridges is demonstrated to (i) be effective, (ii) improve operability and (iii) reduce the carbon loading. This technology can yield a significant process improvement for the carbon treatment step in pharmaceutical applications. Carbon cartridges from two suppliers have been tested in two pharmaceutical API processes. In process 1, the aim was to reduce an impurity (A) from similar to 3% to at least less than 2%. In process 2, the aim was to reduce an unidentified low-level, red coloured impurity (B) to such levels that the Active Pharmaceutical Ingredient (API) would be white to off-white in colour. (C) 2008 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.