Decomposition of gas phase tryptophan (trp) following low energy (<10 eV) electron attachment is investigated by means of a crossed electron/molecular beam experiment. Various negatively charged species are observed, attributed to (trp - H)(-) (203 amu), (gly-yl)(-) (74 amu), HCO2- (45 amu), CN- (26 amu), OH- (17 amu), and O-/NH2- (16 amu). These fragments arise from either simple bond cleavages (e.g., (trp -H)(-)) or more complex reaction involving molecular rearrangements within the transitory negative ion (e.g., (HCO2)(-)). Surprisingly, by far the most predominant dissociation processes occur at sub-excitation energies (below the threshold of the electronic excitation). The present Letter may contribute to a better understanding of the initial molecular processes taking place during the interaction of radiation with living systems. (C) 2004 Elsevier B.V. All rights reserved.