Atomic force microscopy (AFM) has been employed to investigate the surface morphology of [100] cleavage planes of L-arginine acetate crystals. Various step patterns are described and discussed. Morphology changes due to the dissolution of the surface materials by adsorbed moisture in air and recrystallization of the micro-solution are also detected. The detail changes are correlative with the crystal structure. (c) 2005 Elsevier B.V. All rights reserved.