The self-potential (SP) method detects naturally occurring electric fields, which may be produced by electrically conductive mineral deposits, such as massive sulfides. Recently, there has been increasing interest in applying this method in a marine environment to explore for seafloor massive sulfide (SMS) deposits, which may contain economic resources of base and precious metals. Although SMS sites that are associated with active venting and are not buried under sediment cover are known to produce an SP signal, the effectiveness of the method at detecting inactive and sediment-covered deposits remained an outstanding question. We built an instrument capable of recording SP data in a marine setting. We carried out a test of the instrument at the Palinuro Seamount in the Tyrrhenian Sea. Palinuro is one of only a few known sites containing an SMS occurrence that is buried under sediment and not associated with active hydrothermal venting, although diffuse seepage of hydrothermal fluids is known to occur at the site. Elevated electric field strengths recorded in and near the site of previously drilled massive sulfide samples are on the order of . A second zone of high field strengths was detected to the north of the drilling area where gravity coring later confirmed the existence of massive sulfides. Our observations indicate that an SP signal can be observed at the site of SMS mineralization even when the mineralized zone is shallowly buried and active hydrothermal venting is not present. These observations could aid in the planning of future marine research expeditions that use the SP method in the exploration of seafloor massive sulfides.