To obtain ER, one needs to know the concentration of the aerial pollutant under concern at the source and the corresponding air exchange rate through the source. Past experiences have repeatedly shown that it is a formidable task to reliably quantify either of the two variables, on a continuous and extended basis, for CAFO applications. The challenge lies in the harsh nature of the sample air that analytical instruments are not typically designed to handle; high costs of precision instruments; the large number of facilities and locations that must be included in the measurement to make the results representative of the production practices; relatively immobility of the expensive instruments set-up once installed on site; the large number of fans involved for some mechanically ventilated facilities (particularly laying hen houses); the inherent variations in airflow rate among fans due to their conditions of operation (belt tightness, degree of shutter opening, dust on blades, etc.), and high difficulty of determining ventilation rate for naturally ventilated facilities. Nonetheless, the quest continues, for such information has immense implication toward the sustainability of the animal industry. This paper describes measurement and some preliminary results of ammonia emissions from two laying hen houses in Iowa. The work is a part of an ongoing, multi-state project that aims to collect ER data from representative U.S. poultry houses and evaluate the efficacy of certain management practices on ER. The complete objectives of the multi-state project include: 1) to determine ammonia (NH3) emission factors for poultry confinement facilities for representative housing types, manure-handling practices, and seasonal and regional differences typically encountered by the U.S. industry; 2) to quantify the efficacy of selected methods for aerial NH3 emission abatement through dietary manipulation and manure management; 3) to provide research-based information that can be used for establishment of realistic guidelines on NH3 emissions from poultry operations; and 4) to educate industry stakeholders on means to minimize adverse impacts on environmental and natural resources while maintaining or improving production efficiency.