The interactions of copper(II) complexes of kanamycin A with oxidation-susceptible biomolecules: 2'-deoxyguanosine, plasmid DNA and yeast tRNA P h e were studied in both the presence and absence of hydrogen peroxide. The mixture of complex with H 2 O 2 was found to be an efficient oxidant, converting dG to its 8-oxo derivative, generating strand breaks in plasmid DNA and multiple cleavages in tRNA P h e . Some of these reactions may play a role in toxic effects of aminoglycoside antibiotics. These complexes were screened for their antibacterial activity. The microbiological studies undertaken to compare the bactericidal action of kanamycin A alone and complexed with copper(II) ions in both neutral and oxidative environment revealed that the enhancement of bactericidal action by Cu(II) was not statistically significant.