The magneto-tunneling effect was investigated in GaAsAlGaAs double barrier resonant tunneling devices in pulsed high magnetic fiels up to 40T applied parallel(B ‖) and perpendicular (B ⊥) to the barrier layers. In a sample with L z = 50 A ̊ , oscillatory structures due to the 2D electrons in the emitter and the LO phonon assisted resonant tunneling were observed when the magnetic field (B ⊥) was swept at constant bias voltages. A large drop of the current was found in the quantum limit at applied voltages below the negative differential conductivity region. A striking hysteresis was observed in the voltage-current ( V - I) curves. In a wide well sample with L z = 600 A ̊ , rich structures were observed in the V - I curve for B ‖, corresponding to the tunneling to different cyclotron orbits from the emitter.