Preparation of diaminophenothiazinium compounds (I) comprises purification of a diaminophenothiazinium (II) under conditions separating the metallic compounds from (II) or deprotection of the amino group using deprotecting agents devoid of metallic compounds. Preparation of diaminophenothiazinium compounds of formula (I) comprises purification of a diaminophenothiazinium of formula (II) under conditions separating the metallic compounds from (II) or deprotection of the amino group using deprotecting agents devoid of metallic compounds. R 1-R 4 : H, 1-6C alkyl (optionally substituted by halo, 1-6C alkoxy, 1-6C alkylcarbonyl or -CONH 2) or aryl (optionally substituted by 1-4C alkyl, halo, 1-6C alkoxy, 1-6C alkylcarbonyl or -CONH 2), preferably H or methyl R 5-R 1 0 : R 1, F, Cl, Br or I, preferably H X -> : (in)organic anion, preferably Cl or OH R : phenyl/benzyl (optionally substituted by 1-4C (halo)alkyl, halo or nitro), 1-8C alkyl, 1-8C alkyl amino, 1-8C alkoxy, phenyloxy/benzyloxy (optionally substituted on the aromatic ring by 1-4C (halo)alkyl, halo or nitro) and Z : O or S, preferably O. [Image] ACTIVITY : Antimicrobial Antibacterial Immunosuppressive Anti-HIV Virucide Antiinflammatory Hepatotropic Neuroprotective Nootropic Antimalarial Cytostatic Neuroleptic Antimanic Antidepressant. MECHANISM OF ACTION : None given.