In this paper we analyze theoretically the problem of reflection of guided transverse electromagnetic (TEM) mode from a lossy chiral layer located transversely in a parallel plate waveguide. We consider two cases: one where the lossy chiral slab is there by itself (without metallic backing) and the front and the back of the slab are free space regions in the waveguide; and the other where the lossy slab is backed by a perfect conductor. The effects of various parameters, particularly the loss and the chirality of the layer, on the reflected guided waves are discussed and physical insights given. This problem may offer potential applications in the design of novel thin chiral shields and absorbers in waveguides and cavities and also for the study of measurement techniques to obtain material parameters of chiral composites. ¿ American Geophysical Union 1995