Microreactors can perform chemical reactions in tiny channels using continuous-flow processes. The microreactor team at Lonza has designed and tested a series of microstructured devices in continuous-flow plants, and performed lab studies of pharmaceutical reactions with successful transfer to commercial production. Microreactor design and scale-up concept is guided by simple correlations, which are described here and displayed in comprehensive diagrams for hydraulic diameter over typical range of flow rate. This leads to a consistent and straightforward scale-up pathway for single-channel microreactors avoiding parallelization from lab development to pilot-scale production. (C) 2010 Elsevier B.V. All rights reserved.