Abstract: A process for the dyeing and printing of leather and various textile material with developing dyestuffs is described wherein diazo salts and specific 6-membered, heterocyclic coupling components having one ring nitrogen atom especially of the pyridone and pyridine types are applied, the coupling process being independent of the pH-value, i.e. it can be performed with a range of ca. pH 2 to 12, preferably at room temperature so that this is possible not only in alkaline but also in neutral or acid medium, depending on the substrate, and in that it is possible with it to produce with only one of the coupling components by means of variation of diazo salts the whole color range from light yellow to black.