Interest in using ground penetrating radar (GPR) as an inspection tool for wood and wooden structures has increased over the past two decades. GPR provides rapid scanning tool which can provide continuous subsurface information about the structure without the need for direct contact. It is accepted within the steel and concrete industries as a reliable inspection tool. By adapting the GPR for use on wood and wooden structures, the need for an inspector to learn an entirely unique technology is eliminated. Ideally, those familiar with GPR would only need minor instruction on how GPR can be used for wood inspection and hopefully increase the number of skilled inspectors faster than training with a completely unique technology. GPR inspection of wood has been shown to identify moisture, voids, and interior metal. The question remains as to whether GPR can detect internal decay in the absence of water, such as in the case of a covered bridge after a leaking roof has been repaired. This paper reports on a preliminary study, within a comprehensive multi-year effort to investigate GPR technologies, in which the dielectric orthotropy of wood is used to identify regions of interior decay.