The early stage of adsorption of organosulfur molecules on gold and silver was investigated by electrochemical and quartz crystal microgravimetric methods. The potential shifts of the substrate metals, current flowing through the substrates, and the surface mass increase observed during the adsorption process were found to support newly proposed electrochemical mechanisms of chemisorption steps: Thiols adsorb on Au and Ag by an anodic oxidation, whereas dialkyl disulfides adsorb through a reaction that results in net cathodic current. The relative rates of the adsorption depended on the potential of the substrate in accordance with the electrochemical mechanisms. The increase in surface mass due to adsorption was observed to closely parallel the charge expended in the electrochemical reactions.