The electrodesorption of root 3x root3 R30 degrees thiol and sulfur lattices on Au(111) has been investigated by in situ STM and electrochemical methods. For thiol and sulfur adlayers, the root 3x root3 R30 degrees lattice is desorbed in sharp voltammetric current peaks. The electrodesorption kinetics involves nucleation and growth of holes. From the analysis of the dependence of the peak potential (E-p) on the length of the hydrocarbon chain (n), the thiol-thiol interaction results in approximate to3 kJ mol(-1)/C unit. The value of E-p for n = 0 indicates that the S-Au(111) bond energy in root 3x root3 R30 degrees thiol lattices is approximate to 19 kJ mol(-1) smaller, and the bond has a lesser ionic character than the S-Au(111) bond in the root 3x root3 R30 degrees sulfur lattice. Monte Carlo simulations of a desorption model reproduce well the experimental potentiostatic and potentiodynamic results for thiol desorption.