The　chemotherapeutic　agent　cisplatin　was　chemically　linked　to　pGEM-3Zf(-)　plasmid　DNA　to　produce　a　cisplatin-DNA　complex,　Gold　nanoparticles,　which　bind　electrostatically　to　pure　DNA,　could　also　be　added　to　this　complex.　Dry　films　of　pure　plasmid　DNA　and　DNA-cisplatin,　DNA-gold　nanoparticles　and　DNA-cisplatin-gold　nanoparticles　complexes　were　bombarded　by　60　keV　electrons.　The　yields　of　single-　and　double-strand　breaks　were　measured　as　a　function　of　exposure　by　electrophoresis.　From　a　comparison　of　such　yields　from　the　different　type　of　films,　we　found　that　the　binding　of　only　one　gold　nanoparticle　to　a　plasmid-cisplatin　complex　containing　3197　base　pairs　increases　by　a　factor　of　3　the　efficiency　of　the　chemotherapeutic　agent　cisplatin　to　produce　double-strand　breaks　in　irradiated　DNA.　Furthermore,　adding　two　cisplatin　molecules　and　one　gold　nanoparticle　to　DNA　enhances　radiation-induced　DSBs　by　a　factor　of　7.5.　A　number　of　phenomena　could　contribute　to　this　huge　enhancement,　including　the　higher　density　of　low-energy　electrons　and　reactive　species　around　the　gold　nanoparticles　and　the　weakening　of　bonds　adjacent　to　cisplatin　in　the　DNA　backbone.　The　addition　of　gold　nanoparticles　to　cisplatin　and　other　platinum　agents　may　therefore　provide　interesting　avenues　of　research　to　improve　the　treatment　of　cancer　by　concomitant　chemoradiation.　©　2009　by　Radiation　Research　Society.