In this paper we propose a new and simple method for obtaining the ionospheric Total Electron Content (TEC) variations from GPS permanent station data, in a very precise manner and with high temporal and spatial resolution. The key idea is use of the resonant period of 1 sidereal day between the Earth's rotation and the GPS satellite orbit periods, in order to obtain one TEC variation estimate directly from each ionospheric observation. This new strategy can be applied on both global and local scales, for instance to one single station. Its capabilities are shown in the application performed with the data gathered on 17, 18, and 19 October 1995 from 95 GPS permanent stations and 9 and 10 January 1997 (180 stations), coinciding with two major geomagnetic storms.¿ 1997 American Geophysical Union