Pollutants, especially particles, are rarely uniformly distributed within ventilated airspaces due to non-uniform flow field, particle inertia, gravitational settling, and diffusion. Thus, selecting suitable sampling locations for representative sampling is a challenge. The objective of this study was to determine the spatial distribution of particulate matter and ammonia concentrations in a swine building. The spatial distribution of airborne pollutants is not only useful in the design of sampling strategies that require limited sampling locations, but also for the study of pollutant transport indoors. The commercial swine building where the study was conducted was a tunnel-ventilated wean-to-finish facility with a capacity of between 2300 and 2400 pigs. The Total suspended particulate matter (TSP) and ammonia concentrations were measured at 50 and 30 sampling locations indoors, respectively, in December and June. Results showed that the gradient across the length of the building was more pronounced in December than the gradient along the length of the building. In June, the gradient along the length of the building was more pronounced resulting in essentially uniform concentration in a cross section. The spatial distributions of the TSP mass concentration in both December and June were essentially symmetrical about the longitudinal section of the building. The spatial gradient of NH3 concentration was more pronounced along the length of the building during winter. During summer, the spatial distribution was almost uniform except close to the exhaust side of the building. These results suggest that the choice of representative sampling locations indoors would vary depending on the air movement in the building, which is dictated by the ventilation scheme.