In this Letter, we compare the effects of 500 eV electron bombardment on the thermal desorption of benzene (C6H6) and cyclohexane (C6H12) from Zr(0 0 0 1) surfaces. In both cases, unexpectedly high desorption temperatures above 600 K indicate strong adsorbate-substrate interaction. Two desorption states are observed for each molecule, presumably due to tilted and flat molecular orientations. Electron fluence does not significantly alter the amount of desorbing species, but for C6H12/Zr(0 0 0 1) results in small amounts of H-2 desorption near 310 K. Electron bombardment seems to affect the tilted species more than the flat-lying species. (C) 2004 Elsevier B.V. All rights reserved.