This work explores the proposition that magnetic field resonances modulate the transport of particle and magnetic flux in the earth's magnetotail. Coordinated high- and low-altitude measurements during a substorm show periodic variations of magnetic field, plasma density and flow bursts in the magnetotail with frequencies that correlate well with those of magnetic field oscillations at geosynchronous altitude and pulsations measured by ground-based stations. The pulsations' frequency is in the Pc 5 range. The example presented here occurred during the substorm period of May 19--20, 1996, that was chosen as the first ISTP/GGS campaign for the ground-based and theory investigations. There appears to be a resonance between modes sustained by the near-Earth magnetic field and compressional and flapping pulsations that can be sustained by the magnetotail. ¿ 1997 American Geophysical Union