Within the framework of the multi-disciplinary TIPTEQ programme (from the incoming plate to megathrust earthquakes) the aim of deep electromagnetic soundings is to image fluids associated with the subduction of the Nazca plate beneath South America. A combined on-/offshore magnetotelluric experiment was carried out in austral summer 2004/2005 along a profile running perpendicularly to the trench and the volcanic arc from the incoming plate to the Argentinien border between 37.5S and 39S. The ocean-bottom instruments, which were deployed during R/V Sonne leg SO181, incorporate newly developed components (suspension magnetometers and short-span telluric devices based on saltwater bridges) from Woods Hole Oceanographic Institution. A station separation of approx. 30-35 km was chosen for the sea-bottom line while the connecting onshore profile had a station spacing of 10 km. In addition, course networks have been established around active Llaima and Villarrica volcanoes.