The formation of self-assembled monolayers (SAMs) of 6-thioguanine and 6-thioguanosine on mercury from deaerated and air-saturated aqueous solutions has been studied. The self-assembly process was investigated using chronoamperometry, cyclic voltammetry and open circuit potential (ocp) measurements. The presence of dissolved oxygen is a necessary condition for the formation of full SAMs on a hanging mercury drop electrode (HMDE) at ocp. In the absence of oxygen, the formation of such SAMs requires application of an appropriate potential to the HMDE during a certain period of time. The effects of oxygen and applied potential are explained on the basis of the charge-transfer reaction involved in the self-assembly process. (C) 2004 Elsevier B.V. All rights reserved.