Two standard reference materials (SRM), one a nitride powder and the other of an oxide powder, of mean size in the range of 1.0 mu m, were developed to assist in the measurement and analysis of fine size powders. SRM 659, a silicon nitride powder and SRM 1978, a zirconium oxide powder, are intended for calibration and evaluation of instruments used to measure particle size distribution using Sedigraph(R), a gravitational sedimentation method. In the development of these SRMs, the parameters of the powder deagglomeration procedures were studied to determine their effects on the measured particle size distribution of powders. The parameters studied included power output and time of sonication, initial pH of the suspension, and dispersant concentration. The morphology, density, surface area, and surface chemistry of these powders were also measured.