We have solved the equation for magnetostatic equilibrium for an anisotropic plasma pressure; this equation allows us to determine the pressure profile from a given magnetic field. We have used the magnetic field model of Ostapenko and Maltsev [1997>, which is a valid representation of the magnetospheric field for distances ranging from 3 to 10 RE (Earth radii). This model has as parameters the Dst and Kp indices, the vertical component of the interplanetary magnetic field, and the solar wind dynamic pressure. The radial profile of the magnetospheric plasma pressure computed for quiet conditions is close to that obtained from direct measurements. The effect of each model parameter on the profile has been studied. The total energy content for distances from 3 to 10 RE appears to be controlled primarily by the solar wind dynamic pressure. ¿ 2001 American Geophysical Union