The invention relates to a method of printing sheet-form substrates by the inkjet printing process, which method comprises printing those materials with an aqueous ink comprising a) at least one dye of formula ##STR00001## wherein R.sub.1 and R.sub.2 are each independently of the other hydrogen or unsubstituted or substituted C.sub.1 C.sub.4alkyl, R.sub.3 and R.sub.4 are each independently of the other unsubstituted or substituted C.sub.1 C.sub.4alkyl, R.sub.5 and R.sub.6 are each independently of the other C.sub.1 C.sub.4alkyl, C.sub.1 C.sub.4alkoxy, halogen, hydroxy, carboxy, C.sub.2 C.sub.4alkanoylamino or sulfo, X is halogen, hyrodroxy, C.sub.1 C.sub.4alkoxy that is unsubstituted or substituted in the alkyl moiety, phenoxy that is unsubstituted or substituted in the phenyl ring, C.sub.1 C.sub.4alkylthio that is unsubstituted or substituted in the alkyl moiety, phenylthio that is unsubstituted or substituted in the phenyl ring, amino, N-mono-, or N, N-di-C.sub.1 C.sub.6alkylamino that is unsubstituted or substituted in the alkyl moiety and uninterrupted or interrupted in the alkyl moiety by oxygen, C.sub.5 C.sub.7cycloaklylamino that is unsubstituted or substituted in the cycloalkyl ring, phenyl- or naphthyl-amino that is unsubstituted or substituted in the aryl moiety, N--C.sub.1 C.sub.4alkyl-N-phenyl- or N--C.sub.1 C.sub.4alkyl-N-naphthyl-amino that is unsubstituted or substituted in the aryl moiety, benzylamino that is unsubstituted or substituted in the phenyl moiety, morpholino or piperidin-1-yl, and n and m are each independently of the other the number 0, 1, 2 or 3; and b) a solubilizer or a humectant.