New 5-(2-arylethenyl)-1, 2, 4-triazine N-oxide and N, N'-dioxide derivatives were synthesized in order to obtain compounds as selective hypoxic cell cytotoxins. The desired products were obtained when the 5-methyl heterocycle reacted with the corresponding iminium electrophiles. The new compounds were tested for their cytotoxicity in oxia and hypoxia. Some of them proved to be less active in hypoxic conditions than Tirapazamine, 3-aminobenzo[1, 2-e]1, 2, 4-triazine N(1), N(4)-dioxide. Derivative 11, 6-methyl-5-[2-(5-nitrofuryl)ethenyl)-1, 2, 4-triazine N(4)-oxide, was the most cytotoxic compound, but it was non-selective. Some derivatives were studied as DNA-binding agents in oxic conditions showing poor affinity for this biomolecule. This result showed that the cytotoxic activity in oxia is DNA damage not dependent. Electrochemical and ESR spectroscopy studies were performed in order to determine the ability of compounds to produce radicals and the relation of these in the mechanism of cytotoxicity.