The paper gives results of a comparison of several standard materials and techniques for the Warren-Averbach determination of microstructure characteristics of calcium hydroxide--Ca(OH)2--sorbent materials. The comparison is part of an investigation of the injection of dry Ca(OH)2 into combustion streams for the removal of sulfur oxides (SOx). It has been known, for some time, that the reactivity for removal of SOx varies over a wide range for different batches of Ca(OH)2. Because reactivity is a critical factor in the economics of the process, a method to predict the reactivity of Ca(OH)2 batches is desirable. Reactivity can be affected by many factors, including the origin of the calcium carbonate mineral from which the hydroxide is produced, production conditions, and the presence of additives used for reactivity enhancement. It has been theorized that all of the preceding contribute to such physical characteristics as surface area, particle size, and porosity. The examination of these physical characteristics has provided the basis for understanding the reaction processes, but has not provided all the factors necessary to correlate intrinsic sorbent characteristics with reactivity.