Examination of the attack of OH radicals produced in the Fenton way on DNA molecules is important from biological, biochemical, and biosensor points of view. Calf thymus DNA was selected for the investigation, since this natural oligonucleotide is often used in examination of drug-DNA interactions. Particularly useful was the coherent application of five techniques: electrochemical quartz crystal microbalance (EQCM), square wave voltammetry (SWV), circular dichroism (CD), atomic force microscopy (AFM), and UV-vis spectroscopy. These techniques differ in sensitivity to radical concentration and layer thickness of DNA. EQCM appeared to be the most sensitive in monitoring the consequences of OH radical actions; radical activities corresponding to nanomolar concentrations of H(2)O(2) could be detected. SWV and AFM detection gave noticeable signal for higher than 1 μM H(2)O(2) concentrations. EQCM data led to a conclusion that at higher than 1 μM H(2)O(2) concentrations the DNA strands were locally disintegrated. The corresponding DNA loss was ca. 16%. It has been shown that in the presence of α-tocopherol, a strong antioxidant, the damage caused by OH radicals was practically prevented.