CO adsorption and dissociation processes have been studied using first-principles total energy and force calculations. The adsorption energies, atomic structures and vibrational modes of molecularly chemisorbed states are well reproduced in the present calculations. We have examined several possible dissociation paths of CO on Pt(111) and Ni(111) surfaces. The dissociation energy barrier of CO on the Ni(111) surface is much smaller than that on the Pt(111) surface, in agreement with experimental results. (C) 1997 Elsevier Science B.V.