The dynamics of butanethiol and dodecanethiol monolayers adsorbed on Au(111) studied by <i>ex situ</i> and <i>in situ</i> sequential scanning tunneling microscopy (STM) shows, at room temperature and in the range of seconds, √3×√3 <i>R30°⇔c</i>(4×2) transitions. High-resolution STM imaging also shows that these transitions can be explained by a displacement of adsorbed molecules from hollow to bridge sites and vice versa. Transitions from the <i>p</i>(<i>n</i>×1) superlattice to the √3×√3 <i>R30°</i> lattice were also imaged in real time. These processes appear to be coupled with fluctuations of the hole size of the Au(111) terrace.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasFacultad de Ciencias Exactas