The H + H recombination in molecular hydrogen on. graphite occurring according to the Langmuir-Hinshelwood (LH) mechanism is studied in the framework of density functional theory. Graphite was modeled by a single layer cluster and the activation energies were computed for H diffusion and for LH recombination. The influence of the neglected under- and above-lying layers is discussed below for the in-bulk recombination. The occurrence of this mechanism under thermal desorption spectroscopy (TDS) experimental condition is discussed and compared with the well-known Eley-Rideal recombination mechanism. We conclude that the LH pathway must certainly play an important part in TDS experiments. (C) 2002 Elsevier Science B.V. All rights reserved.