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.