In situ scanning tunneling microscopic (STM) measurements of electrochemical processes on 1T-TaS2 in electrolytes containing pyridine and octylamine are reported. Upon stepping the potential from the double-layer regime to -0.44 V, step flow etching is observed in the presence of both molecules. At potentials >= -0.68 V, pyridine intercalation commences, manifesting as an increase in the average layer spacing up to 0.9 nm, followed by an island growth of a second intercalation phase with 1.2 nm layer spacing. These phases are assigned to parallel and perpendicular orientation of the pyridine molecules relative to the TaS2 layers. Deintercalation proceeds via the formation of slowly dissolving blisters, which are attributed to nanoscale pyridine inclusions and results in a network of nanoscale cracks in the surface layer. (c) 2008 The Electrochemical Society.