A method for scaling-up a spray drying process for preparing particles for inhalation from a smaller scale spray dryer to a larger scale spray dryer, relative in size to each other, said method comprising the use in the larger scale spray dryer of a multi-nozzle apparatus comprising single nozzles suitable for use in preparing inhalation powders, wherein the smaller scale spray dryer comprises a number m of nozzles and the larger scale spray dryer comprises a number n of nozzles, and wherein n is determined by scaling m by a ratio, which may be rounded up or down to a whole number, of the drying gas flow rate of the larger scale spray dryer to the drying gas flow rate of the smaller scale spray dryer.