The present article focuses on the cleaning of graffitis on urban buildings by using laser radiation. A comparison between cleaning results obtained with second and third harmonic wavelengths of a Q-switched Nd:YAG laser is presented. Ablation rate studies have been carried out and elemental analysis by laser-induced breakdown spectroscopy (LIBS) has been applied as a real-time diagnostic technique for the cleaning process, with the aim of preventing potential damage of the surface. To remove graffitis on urban buildings the third harmonic was observed to be the most efficient wavelength, supporting the best result. (C) 2002 Elsevier Science B.V. All rights reserved.