Thermogravimetry (TG) and other analysis techniques have been used to study the reaction of mercury with Pt and a Pt-Ir alloy. The results suggested that, when heated, the electrodeposited Hg film reacts with Pt or with Pt-Ir to form products of different stabilities, indicated by at least three weight loss steps. In the first step, between room temperature and 170 degrees C, only the bulk Hg is removed. From this temperature to about 280 degrees C the mass loss can be attributed to the desorption of a monolayer of mecury. The last step, from 280 to approximate to 600 degrees C, can be ascribed to the removal of Hg from a solid solution with Pt and Pt-Ir alloy.