Abstract: A process for preparing a composition having low hygroscopicity, in the form of uniform particles and useful for perfusing artificial kidney systems from compounds to give an electrolyte ion composition comprising Na.sup.+, K.sup.+, Ca.sup.++, Mg.sup.++, C1.sup.- and CH.sub.3 COO.sup.- ions in specified proportions, the process being characterized by dissolving the compounds in warm water, allowing the solution to stand for at least 6 hours and thereafter spray-drying the resulting aqueous solution of mixed salts by spraying the solution into a drying chamber having an inlet temperature of 200.degree. to 400.degree. C. from the orifice of a pressurized nozzle having an orifice diameter of 1.0 to 2.0 mm.