Didecyldimethylammonium chloride (DDAC) is a chemical commonly used in wood protection applications. The penetration of DDAC into wood has implications for efficacy as well as the development of surface analysis techniques such as Fourier transform infrared spectroscopy (FTIR). In order to gain a better understanding of the factors which affect the penetration of DDAC into wood, we saw a need for a technique which can be used to better define the distribution of DDAC within the wood. The technique developed in this project combines a microtome wood sampling procedure with a suitably modified version of Forintek's HPLC method for DDAC analysis. The detection limit was 500ng DDAC per sample vial, or 250ng per 32mm x 7mm x 100µm wood slice. The method was used to profile DDAC distribution in dip-treated wet and dry amabilis fir, Douglas fir, lodgepole pine and western hemlock sapwoods. For all samples tested, detectible DDAC penetration was found to be limited to less than 1mm below the surface. Dry samples were found to retain approximately twice as much DDAC as wet samples, and wet samples were found to retain a higher percentage of their total DDAC near the surface than dry samples. A follow-up study should be done using the techniques described in this paper to analyze DDAC penetration in a larger sample set. The study should compare DDAC penetration in dip, spray and pressure treatments, and should examine the relationship between the penetration of DDAC and other relevant chemicals such as borates and iodopropynylbutyl carbamate (IPBC).