6-Methyl-3-pyridazinone is a lignin-based dye used on wool. 6-Methyl-3-pyridazinone is also used as a reactant for the synthesis of C-(1-aryl-cyclohexyl)-methylamine derivatives as selective, orally available inhibitors of dipeptidyl peptidase IV, imidazopyridazinone derivatives as PDE7 inhibitors and pyridazinone derivatives with an arylpiperazinylalkyl chain as a potentent, orally active, antinociceptive agent.