A wax impregnated graphite electrode coated by linearized plasmid DNA is employed as a sensitive biosensor for the detection of platinum compounds. The sensor relies on monitoring changes in the intrinsic electrooxidation response of the surface-confined DNA resulting from its interaction with platinum compounds and requires no label or indicator. Short reaction times (2-10 min) are sufficient for monitoring submicromolar levels of platinum complexes. It has been suggested that DNA biosensors could be used for quantitating antitumor platinum drugs in various samples including those used when studying mechanisms underlying their antitumor effectiveness.