Newly synthesized phthalazine derivatives including copper and platinum complexes were evaluated forcytotoxicity in human breast cancer cell lines. The cells were incubated with the compounds (100 μM) for 72 h andcytotoxicity, apoptosis and DNA content were measured by flow cytometery. Our results suggest that the parent (H1-2), copper (C1-2)- and platinum (P1-2)-derivatized compounds were relatively more active in inducing apoptosisand cell killing in both human breast cancer cell lines, MDA-MB-231 cells being the more sensitive. Other compoundsshowed weak or no response towards these parameters except H-5 causing 40% apoptosis in MDA-MB-231 cells.Addition of copper or platinum in the structures generally reduced the apoptotic potential. Possible roles for structure activity relationships are discussed.