Abstract Alkylation of some selected [1,2,3]triazolo[4,5-d]pyridazines having five or more nitrogen atoms capable for alkylation was investigated. Pyridyl derivatives substituted also on the [1,2,3]triazole ring gave quaternary pyridinium salts, whereas in the case of the analogues compounds unsubstituted at the triazole moiety, the alkylation of the triazole ring was also observed. Unambiguous structure