In order to prepare basic dyestuffs of the general formula ##STR1## in which A and B independently of one another represent a hetero-aromatic radical or a radical of the general formula ##STR2## in which Ar denotes the grouping ##STR3## in which Y represents hydrogen or a non-ionic substituent andn represents a number between 1 and 4, andR.sub.1 and R.sub.2 represent hydrogen or alkyl, aryl or aralkyl which is optionally substituted by non-ionic or acid groups, or together, or with the o-position of Ar, form a heterocyclic ring,D denotes hydrogen, alkyl, aryl which is optionally substituted by neutral or acid groups, or a hetero-aromatic radical andX.sup.- represents an anion,compounds of the general formula ##STR4## in which A, B and D have the abovementioned meaning, are oxidized with oxygen in the presence of catalytic amounts of benzoquinones which are substituted by halogen or cyano or of phenanthrenequinones which are substituted by nitro, and in the presence of catalytic amounts of nitrogen oxides, with the exception of dinitrogen monoxide, or of substances which produce such nitrogen oxides under the reaction conditions.