It is shown that the introduction of stationary gyrophase bunching in the electron population of a thoroughly stable magnetoplasma brings about strong growth of electrostatic waves propagating perpendicularly to the background magnetic field. We present the first derivation and analysis of the dispersion of these Bernstein-like modes in media exhibiting stationary nongyrotropy, and we demonstrate the occurrence of solutions of the linear initial-value problem with growth rates of the order of the associated real frequencies. ¿ 1999 American Geophysical Union