A completely water-soluble, solid, labile biochemical-containing diagnostic reagent is prepared without the need of a lyophilization step, by spraying, preferably by a fluidized bed process, an aqueous solution of labile biochemical, e.g., an enzyme, onto small particles, e.g., lower than 20 mesh, of an inert, completely water-soluble solid bulking agent, e.g., mannitol; drying the resultant labile biochemical-coated bulking agent to the desired dryness; and then forming resultant dried labile biochemical-coated bulking agent into a tablet suitable for a diagnostic test reagent, said tablet having a predetermined rate of dissolution.