Simultaneous measurements of electrons and magnetic field are used to study the topology of the Martian magnetosphere. Halo solar wind electrons streaming along magnetic field lines replicate variations of the Bx component, thus tracing the interplanetary magnetic field draping in most parts of the Martian tail. This suggests that the magnetic field obserbed near the equatorial plane of Mars is mainly induced. However, there are regions where this perfect tracing is violated. This could be considered as evidence for an intrinsic planetary field. An alternative interpretation involves the relationship between these regions and ionospheric holes. ¿ American Geophysical Union 1994