Viking mission soil analyses and the constitution of the SNC group of meteorites have indicate that the Martian regolith is derived from basalt. On Earth such material often weathers to yield a highly magnetic soil (spontaneous magnetization &sgr;s≥1 J T-1 kg-1), the magnetic constituent of which is fully oxidized titanomaghemite. We propose that titanomaghemite is likewise responsible for the magnetism of the soils on Mars. ¿ American Geophysical Union 1990