Powder processes such as milling and compaction are, in part, dependent on the deformation and fracture properties of the material. Nanoindentation has emerged as a technique that enables the measurement of these properties from very small quantities of sample, including single crystals, thus allowing the possibility of predicting bulk powder behaviour from a few crystals. As a feasibility study, nanoindentation has been used to measure the mechanical properties of single crystals for five pharmaceutical materials, as prepared by commercial crystallisation processes. Young's modulus and hardness were determined by analysis of hysteresis curves. Fracture toughness was determined using an indentation fracture mechanics approach, similar to that applied to ceramics and semi-brittle materials. (C) 2004 Published by Elsevier B.V.