A large-scale ambient monitoring program was conducted in Boise, Idaho, during the 1986-1987 winter heating season to evaluate the impact of residential wood combustion (RWC) and automotive emissions on the local air shed. Consecutive 12-h particle, organic, and gaseous samples were collected at three primary sampling sites and four auxiliary sites to assess the magnitude of RWC and mobile source emissions and spatial and temporal variability among sites. Fine particle mass, fine particle potassium, and fine particle organic concentrations were elevated during nighttime periods at all the sampling sites indicating that RWC emissions were the primary local source. Fine particle concentrations exceeded 100 micrograms/cu m during four winter nighttime sampling periods when RWC emissions were increased, with the highest fine particle concentrations (126.7 micrograms/cu m) observed during a weeday nighttime period. Increased coarse particle, fine particle lead, CO, and NOx concentrations were observed during weekday and daytime periods, indicating the presence of mobile source emissions. An overview of the design and conduct of the monitoring program as well as descriptive summaries of the key findings are presented.