A series of four Cu(II) dichlorides with N-(4,5-dihydro-1H-imidazol-2-yl)azoles as chelating ligands has been prepared and characterized by IR, UV-vis spectroscopy, and X-ray crystallography. The complex [2-(4,5-dihydro-1H-imidazol-2-yl)-1H-benzotriazole]-dichlorocopper(II) showed very potent SOD activity in vitro with a superoxide scavenging IC(50) of 0.06 microM, comparable to those described in the literature for best low molecular weight SOD mimics. Cytotoxicity studies with seven human tumor cell lines in vitro showed that the most active complexes inhibited the growth of cancer cells with IC(50) between 13-28 microM. No obvious correlation was found between cytotoxic potency and superoxide scavenging activity of the complexes in any of the cell lines.