Crystalline forms I and II of 5-amino-2,3-dihydrophthalazine-1,4-dione alkali salt having crystallographic values as given in the specification, determined by X-ray powder diffraction, are new. Independent claims are included for: (1) the preparation of crystalline forms I and II; and (2) a pharmaceutical preparation comprising the crystalline form I and/or II. ACTIVITY : Immunomodulator; Antiinflammatory. MECHANISM OF ACTION : None given.