A new series of N-aryl-4-oxo-1,4-dihydro-pyridazine-3-carboxylic acids has been synthesized by condensation of aryldiazonium with 4-hydroxy-6-methyl-2-pyrone. Some of these compounds exhibited in-vitro cytotoxic activity with moderate to excellent growth inhibition against the murine P815 mastocytoma cell line. Compound 5b showed an important cytotoxic activity against cell line P815 (IC(50 )= 0.40 microg/mL).