The griding chamber of an elliptical fluid energy mill was subjected to further investigations. An operational matrix was established with its elements representing the particular angle between the nozzles giving maximum performance for a given nozzle size and grinding pressure. After estimating the breakage function values for different grinding chamber conditions, it was found advisable, for the best performance with respect to the energy sent in, to follow the diagonal operation in the matrix, with the nozzles being arranged in an ascending order of sizes and descending order for grinding pressures. The effects of the feeder nozzle pressure and the uptake height were analysed by following the process of attaining steady state and by monitoring the pressure difference across the downtake. The results and observations were made use of to develop a circular fluid energy mill, which can be an efficient alternative to the existing mills. The design is patented by the authors under Indian Patent Act. © 1992, Society of Powder Technology Japan. All rights reserved.