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.