[en] Collisionless drift-wave eigenmodes in a sheared magnetic field are analyzed using the WKBJ method. It is found that, for L/sub s//L/sub n/ > (L/sub s//L/sub n/)/sub c/, ion-sound dynamics determines the eigenvalues at small k/sub y/² and the eigenmodes are damped. However, at large k/sub y/², electron dynamics dominates and the eigenmodes become marginally stable. For L/sub s//L/sub n/ < (L/sub s//L/sub n/)/sub c/, the eigenmodes are damped for all values of k/sub y/². The critical value (L/sub s//L/sub n/)/sub c/ scales as (m/sub i//m/sub e/)/sup 1/4/