Adsorption of H (D) atoms on natural graphite (NG) single crystal and highly oriented pyrolytic graphite (HOPG) surfaces was studied with low-energy electron diffraction (LEED) and scanning tunnelling microscopy (STM). No superstructure was observed in LEED, which suggests random adsorption of H on C(0001). Loss of diffraction at increasing H(D) coverage indicates loss of translational symmetry on the surface. STM data suggest that on D covered surfaces randomly distributed C atoms exist which pucker out of the basal plane. Puckered atoms are those which contribute to the STM profile of clean HOPG, i.e., which have no neighbour in the plane below. (C) 2004 Elsevier B.V. All rights reserved.