The structures and spectroscopic properties of new Mn(II), Co(II), Cd(II), Hg(II), Ag(I), Rh(III), and Ir(I) complexes with the ligand BZLMH derived from 6-acetyl-1,3,7-trimethyllumazine (lumazine=pteridine-2,4(1H,3H)-dione) and benzohydrazide are reported. Complexes have been characterized by elemental analyses, spectroscopic studies (IR, UV-vis, (1)H, (13)C and (15)N NMR) and magnetic measurements. In all the complexes, the lumazine-derived ligand appears to be coordinated in either tridentate (N5, N61 and O63) or tetradentate forms (O4, N5, N61 and O63). The molecular structures of the [Co(BZLMH)(H(2)O)(CH(3)CN)(2)](ClO(4))(2) x CH(3)CN and [RhCl(2)(BZLM)(CH(3)CN)] x CH(3)CN complexes, determined by single crystal X-ray diffraction, have allowed to corroborate both coordination behaviours. The cytotoxic activity of the free ligand and complexes against human neuroblastoma NB69 cell line is also described. The differential analysis of the initial cytotoxic screening data has shown good activity only for the [RhCl(2)(BZLM)(CH(3)CN)] x CH(3)CN compound at concentrations at around 2 microM; for the other complexes, a modulation of the cell growth was not found upon complexation, this non-specific effect strongly suggesting an apoptotic behaviour.