A new technique is introduced that remotely measures the plasma density profile in the plasmasphere. Radio plasma imager (RPI) echo observations provide echo delay time as function of frequency, from which the plasma density as function of position along the magnetic field line can be calculated. An example from the nightside plasmasphere (L=3) shows the density having its minimum value near the equator and rapidly increasing densities along the field line above 40¿ magnetic latitude. The density increases at a faster rate toward the ionosphere than the field strength. The index of the power law of the density as a function of field strength increases from a few tenths near the equator to close to unity near 40¿ and greater than 2 near the ionosphere. ¿ 2001 American Geophysical Union