A class of microinstabilities which is likely to exist in plasmas confined in magnetic mirror geometries is examined. These waves propagate across the magnetic field in a homogeneous plasma at multiples of the ion cyclotron frequency. The instabilities are found when all electromagnetic terms are included in the theory. They exist even when&bgr;≪1(perpendicular ion beta) since there are still parametric regions where electromagnetic contributions are larger than the electrostatic terms. Growth rates for a value of&bgr;of 0.01 are of the order of several percent of the ion cyclotron frequency even for loss‐cone distributions that are reasonably well randomized.