We have developed a linear two-dimensional kinetic theory, which is motivated by recent results for the drift-kink instability. The theory predicts plasma instability for large values of ion-electron temperature ratios, Ti/Te, moderate drift speeds, and large ion-electron mass ratios, mi/me, corresponding to conditions in the near-Earth region of the magnetotail neutral sheet. The growth rate predicted by the theory is in good agreement with nonlinear plasma simulations (but the mode structure is not), including linear growth rates obtained with an implicit, electromagnetic simulation with realistic ion-electron mass ratio. ¿ 1997 American Geophysical Union