Recent research has shown that a subterranean termite (Coptotermes formosanus Shiraki) is dependent on dietary nitrogen in order to fulfill it's nitrogen requirements for colony growth and development. Crypototermes brevis (Walker) was chosen as a model for comparison, as it has no access to dietary nitrogen outside of it's wood diet. A full nitrogen inventory before and after colony growth was conducted in order to determine the species' dependence on atmospheric N₂ fixation. In addition, an expression assay was conducted for a gene encoding a nitrogenase subunit (nifH). Nitrogenase expression was then compared between C. formosanus and Cr. brevis. Results showed that N₂ fixation was an important source of nitrogen acquisition for Cr. brevis, and nitrogenase expression was approximately four-fold higher in Cr. brevis than in C. formosanus. The nitrogenase assay used in this study is proposed as a potential tool to measure dependence on N₂ fixation versus dietary nitrogen roles in diverse species of termite.