DNA binding properties of two previously synthesized copper complexes of vic-dioximes bearing thiosemicarbazone units (2E)-2-[4-(dimethylamino)benzylidene]-N-[(1Z,2E)-N-hydroxy-2-(hydroxyimino) ethanimidoyl] hydrazine carbothioamide (1) and (2E)-2-[4-(diethylamino)benzylidene]-N-[(1Z,2E)-N-hydroxy-2-(hydroxyimino) ethanimidoyl] hydrazine carbothioamide (2), were investigated using absorption spectroscopy, fluorescence spectroscopy, and agarose gel electrophoresis methods. Experimental studies suggested that the complexes bind to DNA through intercalation. Their intrinsic binding constants (K-b) were calculated as 1: 5.50 +/- 0.25 x 10(4) M-1; 2: 2.10 +/- 0.18 x 10(5) M-1. These complexes also promote the cleavage of plasmid pBR322, both in the absence and presence of hydrogen peroxide.