It is well known that the majority of active drug substances are delivered to the human body as solid dosage forms. Consequently, a considerable amount of effort has been devoted to the physical characterization of the drugs themselves and, to a lesser extent, the excipients, as it is recognized that the physical state of drugs and excipients can have a major influence on the processing viability, the physical and chemical stability, and the bioavailability of solid dosage forms such as tablets, capsules, and freezedried products (1). The characterization of the physical state of a solid in the pharmaceutical development process is mandatory to obtain a robust formulation and, in this respect, the regulatory authorities require these characteristics to be well documented in any application submitted for approval. Particle size distribution, particle shape (habitus), porosity, surface state and, of course, crystalline polymorphism, are now systematically taken into account in the design of new formulations.