The application of capillary electrophoresis (CE) combined with highly sensitive inductively-coupled-plasma mass spectrometric (ICP-MS) detection allows the interactions of metal complexes with biomols. to be characterized. This technique has been used to provide new insights into the mode of action of the ruthenium-based anticancer drug candidate indazolium [trans-tetrachlorobis(1H-indazole)ruthenate(III)] (KP1019). While the compd. binds rapidly and efficiently to serum proteins, esp. albumin, its reactivity towards the model DNA compd. 2'-deoxyguanosine 5'-monophosphate (5'-dGMP) is moderate.