The lobe and the plasma sheet boundary layer in the Earth's magnetotail are regions of different plasma conditions and share a common interface. The transition from the lobe to the plasma sheet boundary layer is examined here using AMPTE/IRM data. When the satellite crossed from the lobe to the plasma sheet boundary layer, intense narrow banded wave bursts at 1 kHz were observed and then broadband electrostatic noise (BEN) immediately followed. Simultaneous with the onset of BEN, high energy eastward streaming proton beams at >40 keV (>2700 km/s) were detected. These results are used as input into a numerical simulation to study ion beam instabilities in the PSBL. ¿American Geophysical Union 1990