Z mode radiation has been observed in the auroral zones where the plasma frequency &ohgr;p is less than the electron cyclotron frequency &OHgr;e. We explore the possibility that this radiation is generated in the same way as the X mode radiation of the auroral kilometric radiation (AKR), i.e., by cyclotron maser emission driven by a loss cone distribution, specifically by electrons reflected at a lower height and propagating upward. We calculate the growth rate for the Z mode by using a method developed for the X mode and the O mode. We find: (1) Growth occurs in a small crescent-shaped region of &ohgr;-&thgr; space just outside a forbidden zone near &thgr;=90¿ with &ohgr; between &OHgr;e and the upper hybrid frequency. (2) The temporal growth rate for the Z mode is less than that for the (unsuppressed) X mode but comparable with that of the 0 mode; for &ohgr;p/&OHgr;e>0.3 the X mode is suppressed and the growth of the Z mode and the 0 mode compete for the available free energy. Because of the low group speed of the Z mode its spatial growth rate is higher than that of the 0 mode, giving it an advantage. (3) The product of the spatial growth rate and the bandwidth of the growing waves for the Z mode is comparable with that for the (unsuppressed) X mode and is much greater than that of the 0 mode. (4) Although all growing Z mode waves have slightly upward directed wave normals (&thgr;>90¿), most have downward directed rays, many at angles &thgr;g between 50¿ and 70¿, and so can propagate toward regions where &ohgr;<&thgr;e. We argue that these properties suggest that loss cone driven cyclotron emission may be the mechanism generating the observed auroral Z mode radiation.