Substitution of thymidine by 5-bromouridine within DNA sensitizes the nucleic acid to radiation. We show here the ability of low-energy (<12 eV) electrons, abundantly produced along the ionization tracks, to effectively decompose the radiosensitizer via two main fragmentation channels to produce the bromine anion and the 5-bromouracil-yl anion, with a cross-section of 2 x 10(-14) and 9 x 10(-16) cm(2), respectively. The formation of these negative fragments is accompanied by their corresponding reactive radicals, i.e., uracil-yl radical bound to the sugar moiety and 2-deoxyribose-yl radical, which are both considered as precursors for DNA strand breaks. (C) 2004 Elsevier B.V. All rights reserved.