We investigate the role of the plasma mantle in the dynamics of the Earth's distant magnetotail. The plasma mantle can exert a substantial influence on the current-sheet force equilibrium by transporting both momentum and mass from the dayside magnetopause to the tail current sheet. Such influences are particularly strong when the interplanetary magnetic field contains a significant southward component for a prolonged period. We find that a number of processes characterizing a substorm growth phase can be attributed, at least in part, to the plasma mantle. Among these processes are the thinning of the plasma sheet, storage of magnetic energy in the tail, and formation of plasmoids. The rates of these processes are found to increase nonlinearly with the momentum density of the mantle plasma. The present model applies only to the distant magnetotail (x≲-30 RE) because of various approximations that we make to allow an analytical treatment of the governing equations. ¿American Geophysical Union 1990