7,16-Dichlorodianthraquinone-N,N'-dihydroazine (I) ##STR1## is prepared by condensing 1-amino-3-chloroanthraquinone (II) in the presence of an alkaline condensing aid, of an oxidizing agent and of a urea derivative (III) ##STR2## (R: identical or different alkyl groups having 1 to 4 carbon atoms, which may be joined together to form a 5- or 6-membered ring that contains the urea group).
