A multi-state, multi-disciplinary research project is currently underway to quantify aerial ammonia (NH3) emissions from selected US poultry houses with different housing and management schemes. A series of publications will result from this study. This paper highlights the system and techniques used by the participating institutions to continuously measure NH3 and carbon dioxide concentrations and determine building ventilation rate. Specifically, a portable monitoring unit (PMU) has been developed and refined for field measurement and acquisition of NH3 level, CO2 level and building static pressure. Ammonia level is measured with electro-chemical sensors that undergo cyclic purging to avoid sensor saturation. Building ventilation rate is directly measured by calibrating the airflow rates of fans in-situ with a Fan Assessment Numeration System (FANS) device and recording of fans runtime, or indirectly calculated using the CO2 balance method based on the latest metabolic rate information for the modern birds (W-36 laying hens). Comparative tests were conducted between the PMU and a chemiluminescence NH3 analyzer in a field emission laboratory (FEL), and there were no significant differences between the two measurement methods (P=0.33).