Sensitization　of　malignant.　cells　to　ionizing　radiation　plays　a　key　role　in　cancer　treatments　that　combine　chemotherapy　and　radiation　therapy.　Enhancement　by　chemo,　therapeutic　agents　of　DNA　base　damages　and　clustered　damage,　which　ate　among　the　most　detrimental　cellular　modifications,　is　expected　to　contribute　significantly　to　the　radiosensitization　process;　however,.　with　the　exception　of　double-strand　breaks　(DSBs),　no　measurements　exist　on　the　enhancement　of　such　damages　induced　by　the　Abundant　secondary　low-energy　electron　(LEEs)　created　by　ionizing　radiation.　This　lack　of　information　restricts　our　global　understanding　of　the　molecular　mechanisms　involved　in　chemoradiation　therapy.　Here,　we　measure　the　enhancements　of　LEE-induced　damages　resulting:　from　the　binding　of　cisplatin　to　plasmid　DNA　(pGEM-3Zf(-),　3197　bp).　The　enhancement　factors　(EFs).　are　reported　for　base　damages　(WO　on　one　strand　and　clustered　damages;　consisting　of　BDs　and　single-strand　break　(SSBs)　with　adjacent　BIDS　on　the　opposite　strand.　Five　monolayer　films　of　cisplatin-plasmid-DNA　complexes　in　a　molar　ratio　of　5:1　ate　prepared　by　lyophilization　and　irradiated　in　vacuum　with　monoenergetic　electrons　at　the　resonance　energies　of　4.6　and　9:6　eV.　Cross-links,　SSBs,　DSBs　and　the　loss-of　the　supercoiled　configuration　are　analyzed　by　the　agarose　gel　electrophoresis.　Irradiated　samples　are　treated　with　E.　soli　base　excision　repair　endonuclease　(Nth　and　Fpg)　enzymes　to　reveal　by　electrophoresis　base　ModificatiOns　occurring　within　two　helical　turns　of　the　DNA　helix.　From　the　dose-response　curves,　the　total　DNA　damages　induced　at　each,　energy　are　244　+/-　42　and　359　+/-　44　X　10(-15)　electron(-1)　molecule(-1),　while　the　percentages　of　base　modifications　in　these　totals　are　55　and　54%,　respectively.　Binding　of　cisplatin　to　DNA　increases　base　modifications　by　EFs　of　24　and　1.9,　respectively;　these　are　the　largest　finite　EFs　observed:　Enhancement　of　all　lesions　can　be　explained　by　invoking　two　general　mechanisms:　of　electron　transfer　coupled　to　transient　anions　formation　in　cisplatin-DNA　complexes.　The　present　results,　provide　more　complete　information　on　the　radiosensitization　of　LEE-induced　damages　to　DNA　by　cisplatin.