Recent spacecraft observations in the auroral zone have clearly demonstrated the presence of both ordinary mode auroral kilometric radiation and Z mode radiation in this region. Using an electron distribution function measured in the auroral zone, we have calculated the growth rates of both ordinary and Z mode radiation via the cyclotron maser mechanism. The growth rates of the ordinary mode auroral kilometric radiation show that these waves can be amplified at frequencies near the electron gyrofrequency and with wave normal angles at or near 90¿. The magnitude of the growth rate at a given frequency is essentially constant over a wide range of the ratio of the background electron plasma frequency to the gyrofrequency. The growth rates of Z mode radiation, on the other hand, are much more sensitive to the background plasma density. It is shown that in very low density regions these waves are dominant over the ordinary mode. However, as the ratio of the electron plasma frequency over the gyrofrequency increases, the growth rates of Z mode are substantially reduced, leading to the eventual dominance of the ordinary mode over the Z mode. A comparison between the growth rates of Z mode due to the upgoing loss cone electrons and those due to the trapped and ''hole'', as well as the loss cone, electrons shows that the presence of trapped and hole electrons can greatly enhance the growth rates. This study demonstrates that a loss cone alone may not be sufficient to provide substantial amplification for Z mode waves in the auroral zone.