In the classical picture of the polar wind, the H+ flow becomes supersonic and collisionless, and the H+ velocity distribution becomes anisotropic and asymmetric at altitudes above about 3000 km. Previously, the stability of the classical polar wind was studied and found to be stable for a wide range of electron temperatures. However, this classical picture of the polar wind results from steady state models that neglect horizontal plasma convection. The plasma convection at high latitudes can significantly attect the characteristics of the polar wind. For example, ions can be energized in the cusp region and then convected into the polar cap, which subsequently results in energetic ion beams and/or conics passing through the classical polar wind. The effect of energetic H+ beams on the stability of the polar wind was studied with regard to the excitation of electrostatic waves. The cases considered covered a wide range of electron-to-background ion temperature ratios (Te/Ti=0.1, 1, 10) and beam-to-background ion density ratios (nb/(ni+nb)=0.1, 0.5, 0.9). A relatively cold beam was assumed (Tb=0.1Ti). A combination of the Nyquist technique and a direct solution of the plasma dispersion equation was used to find the minimum beam drift velocity required to destabilize the plasma. The following results were obtained; (1) The plasma can be destabilized for relative drift energy ≲1 eV, (2) The plasma is more unstable for large electron temperatures and for comparable ion and beam densities, (3) For large electron temperatures the parallel propagating ion/ion plasma-acoustic instability is triggered first, while the obliquely propagating ion/ion cyclotron instability tends to trigger first for low Te. ¿ American Geophysical Union 1989