When 2,3-dichloro-1,4-naphthoquinone (DCHNQ) (1) is allowed to react with I-phenylbiguanide (PBG) (2), 4-chloro-2,5-dihydro-2,5-dioxonaphtho[1,2-d]imidazole-3-carboxylic acid phenyl amide (4), 6-chloro-8-phenylamino-9H-7,9,11-triaza-cyclohepta[a]naphthalene-5, 10-dione (5) and 4-dimethyl-amino-5,10-dioxo-2-phenylimino-5,10-dihydro-2H-benzo[g]quinazoline-1-carboxylic acid amide (6) were obtained. While on reacting 1 with 2-guanidinebenzimidazole (GBI) (3) the products are 3-(1H-benzoimidazol-2-yl)-4-chloro-3H-naphtho[1,2-d]imidazole-2,5-dione (7) and 3-[3-(1H-benzoimidazol-2-yl)-ureido]- 1,4-dioxo-1,4-dihydronaphthalene-2-carboxylic acid dimethylamide (8).