Ca oxalate was pptd. from aq. solns. of CaCl2 and Na oxalate by micromixing of the reactant streams in the two-perpendicular-jets distributor. The strems continuously collided with each other at 23.5 degrees C, pH 6.5 and ionic strength of solns. 0.2 mol/L. Velocity of the streams were 2.78-11.11 m/s and reagent concns. 0.003-0.05 mol/L. Both immersed and unimmersed configurations of distributors with varying widths of nozzles (0.5 and 1 mm) and horizontal inter-nozzle distances (0, 1.3 and 1.8 mm) were used. The size distributions and hydratation degree of crystals were analyzed. The monodisperse microcrystals of desired form (Ca oxalate dihydrate) and size (1-10 mu m) required for inhalation delivery systems were produced.